it seems to me like it would work better if you did your heavier sets with lower rep numbers first, then moved your rep numbers up and weight down as you go. this is just from my experience, as I have to do my hardest lifts (squats right now) first, otherwise I will NOT have the energy to complete them at the end of my workout.

However, this is just my opinion. Do whatever works best for you!

IMO, lift as heavy as you can every set. If you're looking to warm up, then warm up with just a few reps of a building up weight.

For instance:

my squat routine:

5 reps - 45 lbs
4 reps - 65 lbs
3 reps - 85 lbs
2 reps - 105 lbs
1 rep - 115 lbs

3x5 - 125 lbs

If I was going to increase my weight and I couldn't handle the higher weight, I'd still do the same warm up with maybe a little wider warm up jumps, then do my main set:

3x5 - 130
3x4 - 130

If I'm doing something like dumbbell rows, I don't warm up... all of my sets are the heaviest I can handle to complete 3 sets of 8.

When I feel like I'm ready to increase my weight, I would then do 3 sets of 6 at the heavier weight until I can get 3 sets of 8.

I've been doing the same rep range set up for a while now & i'm looking to change it up.
What i've been doing is 10-12 reps for 4 wks, 8-10 for 4 wks, and 4-6 for the last 4 wks

thinking of doing something like this:
first set: 10-12 reps moderate weight
second set: 8-10 reps heavier weight
last set: 4-6 reps max weight

anyone have any thoughts or ideas? what do you expierenced lifters do? Like i said just looking to change it up. I do a lot of supersetting b/c i only have short stents in the gym...

What you are thinking of doing is exactly what i do. I go for warmup, 12, 8, 6. I start light with a little warm-up set, no or little rest, then up the weight to what I can do 12 reps (sometimes only get 10), then medium-long rest, then adjust weight up and try for 8 reps, longish rest, up the weight and try to get to 6 reps. If I easily got to 6 or even go over, I rest and up it again for a 4th set to try to max out by getting 4-6. Have been at this for a couple of weeks of a 3 month workout plan. So far so good.