Perhaps nowhere in athletics and fitness is warmup more important than in the context of speed training. That's why we utilize The Lifetime Athlete Track Warmup.
This Track Warmup is just one version of a standard activation and prep sequence at the track. It's pretty conventional and similar to what you'll see any high school or college team doing. It goes through a sequence of walk-jog-floor exercise-standing exercise-drill-stride to accomplish two main objectives: get the body amped and ramped up enough to start the main set with good performance potential, and minimize the risk of injury.
I like to keep the warmup very open-ended and I encourage everyone to put their signature on it. Do more or less of any component. Omit, add in, or substitute some of your pet fave movements. The phrase I apply to the warmup is to do as little as possible but as much as necessary. Making these adjustments comes with experience. The colder it is, and the faster you plan to run, the more thorough your warmup needs to be. Easy reps on a hot day won't require as much.
I'll have every athlete use a subjective target of 80% readiness. In other words, keep warming up until you know you could comfortably take off at 80% speed and feel smooth, fluid, and powerful.