I want to know if there is a formula or something to use to plug into my max weight so that way I can rep smaller weight the right amount of times. For example if I wanted to rep 3 sets of 10 or 10, 8, 6. or 5, 3, 1. what do I do?

There are formula, but really, you can tell by just seeing how many reps you can do before you hit failure. Typically, you'll be close to failure by rep 8 if you are lifting 80% of 1rm.

Well, I haven't hit the weights for about 4 years and I came back into it and maxed out at 190 on bench press and I wasn't sure what weights I was supposed to be doing for sets. On my 10, 8, 6 sets I was doing 125, 135, 145, and it is a little off.

The actual weight doesn't matter, only how heavy it feels to you, and how much effort you need to exert to lift it.

I sometimes do drop sets, and by the end, I'm panting like a broken bellows, so that everyone in the gym is looking round at me sweating away with these little dumbbells! How well they wouldn't be looking when I was lifting the big ones!

There are formula, but really, you can tell by just seeing how many reps you can do before you hit failure. Typically, you'll be close to failure by rep 8 if you are lifting 80% of 1rm.

I completely agree... with room for changes.

I've always been weak at the shoulders, for ex.. I'm big in form, but much weaker than id like to be. Doesn't help I've had shoulder injuries, but honestly, I'm weaker there.

But if I can do 75-80% of single max for 8 reps, I'm pretty comfortable with the setup. At shoulders, its just going to be lower for me.

And if it drops lower than that I tell myself I'm spending more time in the eccentric phase so good for me.

I am trying a different approach at it now. I got a workout plan from a personal trainer and it is seems to be effective thus far. I can't lift as much as I used to could because I tore a muscle in my shoulder so I know how that is.