How fast should one change weights? Or When to change weight, after how many workouts?
Me personally, I usually choose a weight that causes fatigue on my last set of reps. Either 5x5 or 3x10. Once that weight becomes easy throughout the set, next time I'll add 5 pounds to each side. I know some people (and I've done in the past) that will go by percentage of max. Maybe someone else can chime in on specific math but it's something like: Bench press-
60% of max x 10
65% X 8
70% X 6
75% X 4
80% X 2 Your next week you'd start at 70 with the same increases.
I'd be careful taking that route and only do so for maybe 2 weeks at a time. Be sure to have a spotter those weeks.