A Short List:
Do assume that your bartender knows exactly what raison d'etre is.
Do Not assume that your degree is higher than the bartender's.
Do wait patiently for the bartender to make eye contact with you before placing your drink order.
Do Not bang your glass, beckon them over with your fingers, or call them by name if they are doing anything else other than standing still.
Do tip on every drink.
Do Not think that once per visit is enough.
Do flirt for free drinks.
Do Not assume that you will get one.
Do engage in conversation, but be aware enough to realize when the bartender is no longer interested in talking to you about Yams or your Mother's trip to Bethesda.
Do become a regular.
Do Not forget your responsibilities as a regular.
Do leave when the bartender politely asks you to.
Do Not force the bartender to impolitely ask you to.
Do Not yell at the bartender when she is on the phone with the owner.
Do Not scream, "I am giving your bar business," at anytime. Your twelve dollars, are not THAT important.
Do bring presents.
Do Not fall in love with the bartender.