As you get deeper into your season, the workouts your coach prescribes will get harder. This is because your coach is trying to prepare you to run your best race(s) at the end of your season, which may be a league championship meet, a sectional meet, or even your state's state meet. These hard workouts - tempo runs, repeats, hill workouts, etc. - are some of your most important workouts of your season.
Treat them like races.
No, that does not mean you should necessarily run them as hard as you do a race. You should run those workouts however your coach tells you to run them. But you need to be prepared for them because you don't want to have that be the day you show up at practice and - oops! - you forgot to hydrate properly, or you ate that greasy pizza slice for lunch only an hour ago, or you're just "not feeling it today."
On the days of these hard workouts, imagine you are running a race at 3:30 (or whatever time you practice). Wouldn't you be extra-sure to hydrate properly on a race day? What would you ordinarily eat on a race day? When would you eat your lunch? Did you go to bed early enough last night?
If your coach hasn't given you a practice schedule, ask him/her what the workout is going to be the day before you do it. Spend a few minutes the night before thinking about how you're going to run it, just like you would if it were a race.
Once you arrive at practice, treat the warmup/stretching/drills like you were about to race. When it comes time to actually do the workout, listen to your coach and do the workout like he/she says.
When the day finally comes to actually run the big race, you'll be ready!