For me this is what I do:
A few sets with the bar so I can lower it well below where it normally sits. This way I can really stretch and get in position properly.
Then I load 1 plate and do 2-5 sets for a few reps just to get the groove going and warm up the muscles. In between warmups with bar and 1 plate I will do leg swings, walking toes touches, fire hydrants etc etc....
I will then put on a 2nd plate and usually just 1 set and I feel good. (Obviously only do this if your 1RM is over 500)
Then once 2 plate feels good and you feel loose and warm I would do something like:
5RM - probably around 85%?
This setup is obviously assuming your 1RM is at least 350+ so you can fiddle around with 1 plate or 500+ so you can fiddle with 2 plates