not really "shots" advice, but something one of my friends used to tell me:
beer before liquor - never been sicker
liquor before beer - you're all in the clear
Drink lots of water before you go to bed (after the night is over) it will help lessen the craziness the next morning (at least it has worked for me!)
I don't do shots anymore... they make me ill.. but I do like mixed drinks!
my favs are long island ice teas, cosmopolitans, appletinis, and good 'ol Malibu coconut rum with sprite!
I hope you have a fun (and safe! hehehe) 21st bday!