Here are the common (and some not-so-common) abbreviations used when writing a prescription. Several apothecary symbols have been omitted because I have no way of representing them, but they are rarely, if ever, used. Please /msg me if I've made any mistakes or glaring omissions.

ac       before meals ("ante cibum")        NS       normal saline, 0.9%
ad       right ear                          1/2NS    half normal saline, 0.45%
ad lib   use as you wish ("ad libitum")     od       right eye
am       morning                            os       left eye
amp      ampule                             ou       both eyes
aq       water                              per      by or through
as       left ear                           pc       after meals ("post cibum")
au       both ears                          pm       evening
bid      twice daily                        po       by mouth ("per os")
BSA      body surface area                  prn      as needed ("pro re nata")
cap      capsule                            q        each, every ("quaque")
cc       milliliter (cubic centimeter)      qd       every day ("quaque die")
D/C      discontinue                        qh       every hour
da, daw  dispense as written                q_h      every _ hours
dil      dilute                             qid      four times a day
DW       distilled water                    qod      every other day
D5W      5% dextrose in water               qs       a sufficient quantity
elix     elixir                             R        by rectum, rectal
fl       fluid                              RL       Ringer's lactate
g        gram                               sig      write on label
gr       grain                              sol      solution
gtt      drop(s) ("guttae")                 stat     stat
h, hr    hour                               SC       subcutaneous
hs       bedtime                            supp     suppository
IM       intramuscular                      susp     suspension
IV       intravenous                        syr      syrup
IVP      intravenous push                   tab      tablet
IVPB     intravenous piggyback              tbsp     tablespoonful
mcg      microgram                          tsp      teaspoonful
mEq      milliequivalent                    tid      three times a day ("ter in die")
mg       milligram                          ud       as directed
mL       milliliter                         ung      ointment
N/V      nausea and vomiting                ut dict  as directed ("ut dictum")
noct     at night

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