Warm-up sets are critical for priming the nervous system and working muscles to be efficient on the work sets. When you warm up the working muscles, imagine that the nervous system is "woken up" to activate the target muscles for the movement patterns you want to perform, ie, which exercise you actually perform.
But there is another category of sets to think about: Feeder Sets. These are done after warming up and pump some blood into the working muscles. When you do this, you feel "in tune" with the movement that you perform.
Feeder sets should be pretty tough, maybe just a few repetitions that fail. What is the difference between these and working sets? Work sets are those that will make you fail, or those that use intensity methods to increase the amount of time spent on the set during the set.
Here's an example of how it all would look like:
Warm-Up Sets  Empty Dumbbell: 20-40 Simple Repetitions
Feed and work sets
- Fourth set: Add weight (from last warm-up), 8 reps, pause 120 seconds
- Start now with your work sets, regardless of their repeat range.
No-nonsense warm up exercises for large lifters
30 minutes to the fair