If, for some reason, you are limited to only yourself (a bassist or drummer) and your partner (the latter,) don't feel like you can't rock! You might initially think that you need additional vocalists, guitarists, and the like, but really, all you need is right there, with the addition of some minor equipment.
I'll be writing from the bassist's point of view.
To simulate most rock sounds of the day, you really don't need a guitar. Most hard rocking guitar is just power chords anyway, and these can easily be played on your bass.
- Learn to transpose guitar riffs and licks to bass.
This is very simple. The bass guitar has 3 complete octaves to work with, so all you have to do is take it down a notch and work out the fingering. Alot of your fretting will take place above the 12th fret with guitar stuff, so you might want to practice with that stuff.
- Learn how to play chords on bass.
This is also easier than it sounds. Most power chords use the same notes as your minor pentatonic scale. Using your forefinger and ring finger, just fret the root, fifth, and eighth of whatever chord you're trying to play. Playing this clean sounds a little overbearing, so we'll move on to #3.
- Use Distortion when needed.
A good distortion pedal (like the Boss DS-1) will only cost you about $50 and will do you a world of good for simulating a guitar. If you really want to spring the big bucks, you can get a truly awesome MXR M-80 Bass DI Box for about $150 that will not only give you awesome distortion, but will have customizable EQ and Gate settings to enhance your sound. When using power chords and strumming (I'll detail in #4,) distortion will make your bass sound just like a guitar, only stronger. Distortion also comes in handy for doing wild guitar solos without your audience stopping to realize that there's no guitar onstage.
- Strumming on bass.
There are two ways to strum on bass: (a) Use a pick or (b) Use your fingers. I strongly, strongly recommend against using a pick for several reasons. When using a pick, you change alot of your bass's unique tone, you complicate your life when you want to throw in some slap, and you make other bassists scoff derisively when they see you play. Unless you have to, try to stay away from using a pick.
Strumming with your fingers is very easy. First, hold a pick in your hand. Now, take the pick out of your hand, but keep your fingers clinched as if it were still there. With this position, you can strum with the back of your forefinger's fingernail on the downstroke, and the back of your thumbnail on the upstroke. This makes a nice clicking sound and is great for playing chords.
- Vocals.
All you've got to do is mike yourself and your drummer (provided you both know how to play and sing at the same time) and you're good to go.
With this simple 5-step procedure, you can rock as hard as a 5-piece band even though you only have two members. Enjoy!