I was a bartender from second year university until I got my first full-time teaching gig. I started the year the movie Cocktail came out, and I spent hours and hours practicing the various tricks, with zero sense of irony. So I have loved watching the rise of the cocktail in recent years.
When I bartended, 75% of alcoholic orders were:
1. beer
2. highballs
3. wine
4. Shooters, mostly sambuca, tequila, jagermeister, B52s, or the stag/stagette party triumvirate: orgasm, sex on the beach, blowjob.
Of the remaining 25% that could reasonably be called "cocktails," almost all of them were:
1. Caesars (the Canadian Bloody Mary)
2. Margaritas/Daquiris, almost always blended
3. Chi-chis/Pina Coladas, almost always blended
4. Long Island Iced Tea.
5. Fruit Punch variant (Tequila Sunrise, Planter's Punch, Mai Tai, etc.)
6. Martini variant
7. White/Black Russians
Every so often you might have to get out the little cocktail book for something else, but honestly you could work for weeks just knowing how to do the drinks listed above.