I'm thinking of doing SS as almost all of you recommend it. Also quick question-After you get accustomed to lifting a certain amount of weights, when should you change your weights to do a heavier set?
It doesn't work like that. SS is a linear progression. It means that each workout is always going to be heavier than the last.
When you begin the program, you have to pick your starting weights. You start with just the bar to warm up and get a feel for the movement. Then you gradually add weight, probably in 10lb increments. Do this until you find a weight that is challenging, but not heavy enough that you have to grind it to do three sets of 5 reps with that weight.
So suppose your starting weights look something like this:
Squat 100lb
Bench 85lb
Press 65lb
Deadlift 135lb
Your first SS workout (assume it takes place on a monday) would be called "A" and it would look something like this:
Squat 100lb 3x5
Bench 85lb 3x5
Deadlift 135lb 1x5
These are your working sets. Working sets are 3 sets of 5 reps accross (with the exception of the deadlift, which is only 1 set of 5), which means you don't change the weight between sets. This doesn't include warmup sets. For a 100lb squat, for instance, it would look like this with warm ups:
45lbx5
45lbx5
75lbx3
100lbx5
100lbx5
100lbx5
The next workout (on Wednesday), which we'll call "B" would look like this:
Squat 110lb 3x5 (we've added 10lb since the last workout)
Press 65lb 3x5
Chinups (3 sets of as many reps as possible).
Then on Friday we repeat "A", except it's a bit heavier:
Squat 120lb 3x5 (we've added another 10lb)
Bench 90lb 3x5 (we added 5lb since monday)
Deadlift 145lb 1x5 (we've added 10lb).
So this week we've done ABA, and next week we'll do BAB, etc. And every workout we're adding weight to the bar. At first you'll be adding 10lb to the lower body lifts per workout and 5lb to the upper body lifts. After a while, that'll have to change and you'll be adding 5lb per workout to the lower body lifts, and 2.5lb to the upper body lifts.
For further information:
http://startingstrength.wikia.com/wiki/FAQ:The_Program