Warm-ups here don't refer to quick side bends, hamstring stretches and shoulder circles. There is a certain method to appropriately warming up for each strength training exercise. It's not complicated: Start light and ramp your way up. Then as weight goes up, your reps go down.
Image by JamJammy.
Your warm-up sets are designed to make your "real" working sets consistently your strongest and best for that session. That's how you know if you're getting stronger and improving over time. But how do you know when you're ready for your working sets? Unfortunately, it varies based on the training session and your training experience, but Unapologetically Powerful at least gives this general template that you can use and adjust to suit your individual workout:
1×10 with an empty bar
Work sets commence!
Each successive set should be heavier. Notice that the reps go down as you pile more weight onto the bar. Also, you don't need as many warm-up sets for three sets of 10 reps, versus three sets of one rep. And one of the most important things to understand is that "heavy" isn't always just the actual kilograms on the bar. It could also be what feels heavy for that day.
How to Approach Warm-up Sets [Unapologetically Powerful]