When I was going to the gym, the instructors there always told me something that made alot of sense, and I kept at it:
Do a stretch, and then a little cardio as a warm-up, but no more than that.
Then do your resistance training according to the goal you want to.
always include a little resistance on legs/back even if that's not your program
Then do cardio for half an hour to 1 full hour, maximum.
The reasoning was:
stretch --> necessary, but don't overdo it
warmup--> get the blood flowing (and oxygen) so you can go all out on resistance
cardio after --> because during resistance, you should have burnt up all the sugars in your blood, meaning if you do an aerobic cardio, you'll be able to start burning body fat much quicker.
and 3 times a week, at interval mon/wed/fri. Meaning you gave your body time to recover after workout.
It did give me some great results, back then. I should try and follow that again some time soon
