I’m a sports-performance coach. For 20 years, I’ve been hanging around in gyms, coaching thousands of football, basketball, and track-and-field athletes on how to build muscle and lose weight. I show up before the gym rats and leave after they jump ship. And that means I’ve seen every mistake that is humanly possible to make. Stupid mistakes. Dangerous mistakes. And maybe worst of all, time-wasting mistakes.

Time is always a crucial factor, whether a guy is trying to survive training-camp cuts or hustling back to the office before the boss puts him in for the next round of layoffs. Save a minute, add more muscle. It’s a principle you can build on.

Here are the most common mistakes I see in the gym. Let this be the last time I warn you.

You Don’t Use a Training Log

It’s hard to break records that don’t exist. So invest in a clipboard. Then focus on lifting more total weight each workout. It’s the key to building muscle. Here’s how: Multiply the amount of weight you lift for each exercise by the total number of times you lift it. Then increase that number every workout by moving heavier weights, increasing your repetitions, or doing more sets. So if in your last workout you did three sets of 10 repetitions of the bench press with 150 pounds, your total to beat is 4,500. Accomplish that goal by doing four sets instead of three, 11 repetitions instead of 10, 155 pounds instead of 150, or a combination of the three.

Beginners take note: Training logs aren’t just for the big fellas. In a 2002 study, YMCA researchers found that 70 percent of exercisers who set goals stuck with their programs for the entire year. By contrast, three-quarters of those who didn’t set goals dropped out.

You Try Too Hard

Working your muscles to failure—the point at which you absolutely can’t do another repetition—isn’t the best way to get bigger and stronger. As your muscles fatigue, they use fewer fast-twitch fibers, which have the greatest potential for size and strength gains. For most exercises there’s an easy fix: You can simply use a weight that allows you to finish all of your repetitions.

But body-weight exercises like chinups don’t allow that luxury. The solution: Cut your repetitions in half and double the number of sets you do. So if you can do only three sets of four chinups, you’ll switch to six sets of two repetitions. That way, the total number you do is the same as in your typical three sets of four, but you’ll focus your training where it counts the most—on those fast-twitch muscle fibers.

You Have a Big Ego

Don’t feel terrible if you’re guilty of trying to lift more weight than you can handle. It’s a product of our natural inclination to be better than the other guy. (If we can’t have his job, his house, or his car, we can at least outlift the smug bastard.) But the only way heavy weights benefit your end goal is if you lift them with perfect form. Item #5, on the next page, describes a few of the signs that you’re working with more weight than you can handle. Some less obvious clues:

You can’t perform an exercise through its full range of motion. For instance, on a squat, you know you should lower your body until your thighs are parallel to the floor. But if you’re using too much weight, you don’t dare go down that low for fear of getting stuck, so you stop halfway and then return to the starting position.

You can’t do your entire set without the help of a spotter. You should always have one on hand for your maximum-weight sets, but he’s there for safety, not to actually help you perform your repetitions.

You can’t hold on to the bar without wrist straps. Straps are effective if you use them occasionally, but many men use them on all their sets to mask weak grip strength. You’re better off using weights you can hold without assistance, and forcing your grip strength to improve along with muscle size and strength. Trust us: Lift without straps and soon you’ll be lifting more than you ever could with them.

Your lower back arches like a sapling in a windstorm on bench presses and arm curls.

Universal ego-fixing drill: Once a month, do 10 sets of a single repetition of an important exercise such as the bench press, squat, or deadlift. Use about two-thirds of the maximum weight you’re capable of lifting on that exercise. If possible, have a trainer or knowledgeable friend evaluate your form. Strive for perfection on each repetition. Once perfect form for that exercise becomes second nature to you, you’ll reap greater gains—with fewer injuries—from your normal workouts.