On these back workouts I get the blood flowing by whacking a punchbag for a few minutes, then I do a variety of low weight warm up moves that mimic the first exercise, then it's half the working weight and then the working reps. I find that's the best way to prepare my aching, often damaged, knackered lower back without stressing it too much.

For other body parts I used to do the sort of standard three light warm up sets but since reading a post by CC (don't know what one offhand) that says . . .
"The first warm up set serves to bring blood to the muscles and joints.
The second and third warm up sets are an approach to the weight of the first working set.
The interplay between the muscle and nerve is stimulated, meaning the athlete gets a feeling for the heavy weights without wasting strength and energy at the same time.
During the following exercises the warm up sets are completely omitted which means that they are only necessary for the first exercise of the muscle to be trained.
Do not forget, however, that during every exercise or set you should try to squeeze out an additional 1 or 2 reps more than the previous session in order to increase training weights the following week.
The continuous tire-some struggle to increase reps and weight is the only way to build a massive body:
Always remember: HEAVY WEIGHTS BUILD BIG MUSCLES."
. . . I've started warming up like that. I find it really helps to hit the exact right weight for the working rep!

I hope that makes sense.

Two new fish - different sides of the pond!