this is what i do...

1) find ur 1RM (let's just say 200#)

2) to find your workout load, take 80% of ur 1RM -> 160#

3) to find your warmup sets, take (50%, 70%, 90% of your workout load)

4) so basically it'll look like this:

Warm-Up:
10 reps x 80#
7 reps x 110#
5 reps x 145#
Workout Load:
10 reps x 160#
10 reps x 160#
10 reps x 160#

-if you are just starting you may want to start w/ less than 80% of your 1RM because you'll tire easy and you want to make sure you keep goin up each week and not crash... aka also keeps you motivated by goin up in weight each week.