Isabeal Jupiter gave tips on how to not get picked up in Second Life.
I find some of the tips useful. I am speaking from my personal experience. Wearing revealing clothes will get you picked up but is dependent on the place where you are in. Being strange will deter people too (yes it will). However, I find it hard to abide to all the tips. I am not a very sociable person but I find it hard not to socialise at all.