There's no single way to do it. I like to pyramid up, starting with warm-up sets. And I hate to go down from the weight I used in the first set.

So let's look at several different set-rep combinations, and how you might proceed:

In the first example, let's say you're doing 3 x 15 (3 sets of 15 reps). You decide to use 15-pound dumbbells on the first set, which is basically a warm-up. You get all 15 reps easily.

You go up to 20 on the next set and, again, you get all 15 reps, but you don't feel as if you could get close to 15 reps with a heavier weight.

So you use 20 again, but this time you don't even get 15 -- you have to stop at 12 or 13.

That's probably the best you could do with that configuration, since the higher the reps the harder it is to predict the appropriate load. Fatigue is a much bigger wild card.

You asked about 4 x 10. Here's how I'd approach that:

I'd probably do a warm-up set with a light weight, maybe two-thirds of what I planned to use in my first work set, and I'd stop at about 8 reps. This is just to practice the movement. (And if it was late in the workout, vs. the first exercise, I wouldn't even do a warm-up.)

The first work set would also function as a second warm-up set. Let's say I use 100 pounds, and get all 10 reps easily.

Next I go up to 120, and get the 10 reps, but the weight feels a little heavier than what I'd expected. I use that weight again for the final two sets, but I get just 8 and 7 reps.

That's not ideal -- I've overshot with the weight. But I'll also get two or three more chances to repeat that workout before I finish the program.

In the second time doing that workout, I'd use the same weight, with the goal of getting all the reps in every set.

The third time, I'd do something like this:

Set 1: 100 pounds x 10 reps

Set 2: 120 pounds x 10 reps

Set 3: 125 pounds x 10 reps

Set 4: 125 pounds by ?? reps

The fourth time, it might look like this:

Set 1: 100 pounds x 10 reps

Set 2: 120 pounds x 10 reps

Set 3: 125 pounds x 10 reps

Set 4: 130 pounds by ?? reps

In other words, find ways to keep maneuvering upwards toward heavier loads.

The first time you do a workout in a new program, be conservative with the weights you select, since it's easier and more effective to move up on subsequent sets and in future workouts, rather than starting too high and pushing yourself too hard at the start of the program. You want the big, push-your-limits workouts to come at the end of a program, not the beginning.

I hope that helps!

of an answer but i usually pick a goal weight like 150 pounds then start at 100 pounds and each set at ten pounds, but i agree with lou its never good when you have to work down