The longer you take to warm-up on your initial movement, the better your working sets will feel, and starting with the empty bar to see how your body is feeling on that day will tell you a lot early on. Get to the point where you can tell, just by using the empty bar, whether the training session is going to be on point, average, or sucky.

Using an empty bar will allow for some instinctive regulation in regards to loading patterns, rather than just sticking to an outlined routine. If you're scheduled to do heavy-ish sets of 5 but can tell through your empty-bar warm-up that something feels tight or off, lower your intensity for the day and do more volume with a lighter load. This has saved my ass on more than one occasion in regards to avoiding injury, and it'll save yours too.

Empty Bar Warm-Up Rules

1. Treat the warm-up with respect. Set up for empty bar warm-ups the same way you do for your biggest sets. In other words, set up like it's heavy.
2. Treat the reps the same way as well. Yes, an empty bar will feel light. But doing kipping empty-bar reps where you're flailing all over the place is dumb. Use smooth reps. Pay attention to what your joints feel like and how your body is moving. This will give you some clues about the rest of your workout. Does it need to be adjusted? The empty bar will let you know.
3. Do 2-4 sets of 20-40 reps. Yes, that's a wide range. If everything feels great after two sets, add some weight. If you still feel stiff after two sets, no one said you have to start adding weight. Take as much time as you need with the empty bar until your setup, technique, and rep execution feels dialed in.