Sex is not necessarily something undertaken after measured consideration of the options, for which reason much that has been written on the subject on the assumption of rational discussion and forward planning may be of little help in real life situations. Sex is a need, an urgency, the feeling that every square inch of your body is a country that needs to be colonised with my lips, my skin and my flesh and if I have to wait any longer to get my hands on you I may have to take you here and now in the middle of the road. But even if you are feeling that you may burn up if you cannot touch that dazzling body, even if you are feeling you may melt because you have, there are still some general rules of common courtesy which will help you to carry on feeling good about yourself and comfortable with each other when you find your way to that soft spot afterwards where you rebuild the bed, wipe the stains from the walls and help each other to find your socks and telephones.
Hygiene
They used to say that cleanliness is next to godliness. Studies have even shown that people who have done something bad feel better about themselves if they wash afterwards. Sex is something good, and so people often feel better if they wash beforehand. However, washing can take up valuable time that could be spent in more interesting ways. One possible solution to this problem is the shared shower or bath, which can also provide useful opportunities for enjoyable foreplay or even the act itself. Bear in mind when sharing washing water that whatever your habits when alone, you should think twice (at least) before peeing in company. If you feel you know your co-washer well enough, you should ask for permission, possibly referring briefly to the beneficial astringent effects of urine applied to the skin. Here, as ever, a no is a no. Nonetheless, if you do pee clandestinely without being discovered, do not feel that you should 'come clean' and confess. Urine has a beneficial astringent effect when applied to the skin, so no harm has been done, and for some people being told that they are bathing or paddling in pee can be a big turn-off.
Given that washing immediately before sex is not always desired or practicable, it is advisable for the sexually active to wash regularly. However, after a long day, even the most hygienically conscientious may find that, through no fault of their own, crucial parts of their body are no longer in an optimal state of fragrance. Should you find yourself in close proximity to such a body part with the intention to make oral contact with it, you may find this off-putting. Under these circumstances you should not make disparaging comments, such as "how long has that been ripening!", which are likely to lead to an undesirable cooling of the atmosphere. Instead, take action to remedy the situation. Remember: slobber is your friend! Manual manipulation is always welcome as a prelude to labial contact, and if you dribble on the parts concerned before and while handling them, it is a trivial task to clean them to an acceptable degree. Drooling is better than spitting, which is unappetising and only appropriate if you are making yet another bad porn film. So: saliva on hands and bits, hands on bits, wipe hands discretely on sheets and/or neighbouring thighs, repeat as necessary, dive in, bon appetit.
It may happen that your partner's enthusiasm is great enough to overcome any aversion to the odours of the day, and that after an enjoyable interlude of passive muff-diving you find that the stonk formerly confined to your privates is now liberally distributed around a happy face with a clear intention of kissing you. Once again, verbal expressions of disgust along the lines of "eeuw, your kisses smell of wee!" are likely to be counterproductive. Bear in mind that this is your pee, acquired in the process of worshipping you in the most sincere fashion possible. An amused smile followed by a wipe or two with a slobbery hand is one option; if there are washing facilities nearby, a polite request to use them is another. An undertone of shy embarrassment may well be appreciated in such a request. When the face is once again presentable, make sure that your kiss is thorough and appreciative.
Oral considerations
Much ink and many bytes have been spilt on the question of the correct diplomatic procedure to be followed in requests for oral sex. But a blow job is like credit in a bar: it is better not to ask for it, as a refusal often offends. If your paramour does not spontaneously go south with the mouth, your best option is to lead by example. Judicious (but not intrusive) distribution of your anatomy while doing so should leave the relevant portions in easy reach should inspiration strike the recipient of your adulation. But do not rely on the spirit of give and take to lead to any specific outcome. Sex is far more than a simple exercise in tit for tat. You may not get tat for your tit (as it were) this time, but there is more than one way to skin a cat (as they say).
Should you be engaging in oral stimulation of a person with a penis, you may find yourself faced with another of life's perennial questions, raised in saga and song since the dawn of time: to spit or to swallow. As noted above, spitting is in any case unappetising, so the question is better posed as 'to dribble or to swallow.' If you do not wish to consume semen (perhaps you are on a diet, or it is contrary to the tenets of your religion) then a useful option is to continue gentle oral and manual stimulation while allowing the ejaculate gradually to escape from your mouth and discretely spreading it around. Thus you can rid yourself of unwanted protein without causing offense, and indeed while continuing to give pleasure. Another option is to use the so-called 'ferret in a fox-hole' technique: when it is clear that there is no turning back, stimulate the top end of the organ with a rapid flapping motion of your tongue. The result will be total ecstasy on the part of the flappee and spunk more or less everywhere but in your mouth. However, the option most likely to bring forth cries of glee and (at a later stage) sincere expressions of admiration is the deep throat technique. If appropriately applied with reasonable timing this can leave you with a slight odour of hard-boiled eggs in the back of your throat and every drop of ejaculate tidily and diplomatically accounted for. I recommend practising with a banana. Carrots are too hard.
The 'spit or swallow' question is orders of magnitude less likely to arise when pleasuring a woman than a man, although given the quantity of ejaculate it may feel subjectively more urgent if it does, despite the milder taste. Should a woman ejaculate in your mouth, the appropriate procedure is to find a small clean sealable jar, fill it with the fluid, and send it to a reputable laboratory for analysis so we can finally find out what that stuff is made of.
Hair
In the olden days of say, fifteen years ago, the shaving of the pubic region was a perilous undertaking and the hairy bush was the norm. Specialist pornography was available for those perverts who preferred bare skin. Then the Gillette company spent a billion dollars developing a razor blade that was sharp in one direction and soft in the other, and the total acreage of intimate afforestation of the developed world entered into free fall. Specialist pornography is now available for those perverts who prefer hair. Far be it from me to express an opinion on the respective merits and drawbacks of the Delta of Venus and the plucked chicken, still less to consider the silliness of the landing strip or the implicit agony of the full Brazilian. I shall simply note that hair is soft, skin is smooth, and stubble is neither.
Alternative orifices
If you and the object of your desire are both male then only one suitable orifice is available for penetrative sex, and there will normally be no difficulty in establishing whether this is desired. If you are male and your partner is female, there is generally no immediate necessity to consider the penetration of any orifice other than the conventional one, which is eminently well suited to this purpose. However, availing yourselves of the alternative opening may on occasion give her pleasure. Should she desire to partake of this pleasure, she will doubtless find ways to move in such a way as to encourage you to provide it. But what is the courteous and decorous way to encourage her to feel this desire, if she has not previously considered it? Before addressing this question, consider your reasons for asking it: are you merely looking for variety in your jaded life; do you in fact consider the act perverted and wish to take pleasure in transgression? If so, give the idea up, unless you are making yet another bad porn film. If your motives are pure, begin your research and encouragement with your fingers. If your initial exploration leads to a more in-depth investigation, remember to keep your eyes on her face. This will make her feel valued as a human being, and may also give you an opportunity to enjoy some unfamiliar and possibly entertaining facial expressions. If you are unsure whether they are positive, there is no harm in asking. If her eyes pop out of their sockets and she holds you in a vice-like grip, then you are probably doing something right. Do not complain if you end up with pooh on your willy, just go and wash it off. You need to wash it anyway. And why weren't you wearing a condom?
If you have been on the receptive end, and find that things are painful when the dust has died down, refrain from complaining bitterly. A rueful comment to the effect that 'maybe we should have taken a little more care' should be sufficient to get the message across. Next time, if you want a next time, he will take things more slowly and lubricate more thoroughly. If he doesn't, consider encouraging him to leave.
Unusual tastes
A certain kind of bad preacher exercises pressure on his (it is seldom a her) flock by claiming that if you truly believe then you will do something that they regard as a Good Thing, such as smiting the unbelievers, shunning the heretics, voting for bigots, or giving him money. The sensible response to this kind of pressure on the part of those who feel no inclination to do such things is to conclude that they are not true believers.
Similarly, if somebody tells you that if you really love them then you will do something that you feel no inclination to do, the conclusion to be drawn is obvious. Bearing this in mind, it is not only discourteous, but may also be unwise to attempt such persuasion yourself.
Godlike powers
You have taken the course or read the book, you have done the exercises with dedication and discipline, and you now have astounding oriental muscle control and can maintain your erection for hours on end/break eggs and shoot bananas across the room with your vagina/elicit an orgasm in any part of another person's body with the tip of your little toe. But now you are interacting with a mere mortal. Bear in mind that there may be limits to their endurance. There is no shame in finishing after only an hour and a half if your partner is fainting or gasping for mercy. (You should in any case consider scheduling a break after the first two hours, to assess the situation and check for damage.) Similarly, you should not be offended if your amazing turbo-powered pump-action vagina fails to revive the fading rigidity of your extenuated stud.
Of course, if you have the good fortune to seduce another such demigod as yourself, you may be in a position to address the theological question of what happens when an irresistible orgasm meets an indefatigable erection. But remember: this is meant to be fun; it's not a competition.