A good warm-up sets the tone for your whole workout. A bad one wastes time and can even impair the performance in the main workout. I have five rules for a winning warm-up:

  1. Ditch the general warm-up phase. Traditionally, the warm-up consists of the general warm-up, such as walking the treadmill for 10 minutes before squats, and the specific warm-up – lighter sets that precede your working weights for the day. But unless you're an 85-year old arthritic about to clean and jerk up to a daily max at 6 AM on a cold winter day, skip the general stuff and get right down to business. While general warm-up activities do indeed "warm you up," they don't allow you to rehearse the skills involved in the lift you're warming up for. So it's better to kill two birds with one stone. If you're warming up for squats for example, start with some bodyweight or light goblet squats to wake up your knees, then put the bar on your back and start rehearsing for the main event.
  2. When your warm-up weights are still light, don't rest 3-5 minutes between sets like you would with heavy weights. This is just a waste of time and leads to distraction and procrastination. At the very least, use the time between these early warm-up sets to stretch or foam roll.
  3. Your last warm-up set should be a "prep set." Its sole purpose is to help bridge the gap between your last warm-up set and your first work set. Here's an example using a squat workout:

    45 x 5
    95 x 5
    135 x 5
    185 x 3
    225 x 1
    275 x 1
    315 x 1
    345 x 1 (Prep Set)
    385 x 1 (Work Set)
    275 x 8 (Back-Off Set)
  4. Merge your warm-up sets for the next exercise with your work sets for the current exercise. Example: If you're currently deadlifting and your next exercise is weighted chins, there's absolutely no reason why you can't do a few easy sets of chins between your last few work sets on deads – you're using entirely different muscle groups after all. Then, when you're done pulling, you move straight to your work sets on chins.
  5. Stack exercises. This isn't a warm-up tactic in the purest sense, but using it does reduce your warm-up time. Essentially, exercise stacking means ordering your exercises in such a way that each exercise becomes a warm-up for the exercise that follows it.

An example from the sport of weightlifting would be a workout consisting of cleans, followed by clean pulls, followed by deadlifts. A lifter who has a max clean of 250 pounds can start his pulls with 275, and start his deadlifts at 315. Similarly, previously performed chins can reduce or eliminate warm-up sets for curls, and bench presses can all but eliminate the need for warm-ups on triceps movements.

Related:  7 Ways to Make Your Training Efficient

Related:  The Perfect 6-Minute Warm-Up