As you go about your business in the weight room, have you ever glanced over at a personal trainer during one of their client sessions and idly asked yourself something like, Dang, I wonder if they ever happen to notice what I'm doing over here? Good news! While your gym's fitness professionals obviously can't leave their charges to deliver you some kind of stern pro bono talking-to, they do see you, and they have a lot of feelings to share about... all the myriad things you're doing wrong. (Perhaps this is, in retrospect, one of those questions to which you didn't want to know the answer.)

Fortunately, a few trainers have generously agreed to share with us the most common and most aggravating habits they see gymgoers developing—and a little free advice on how to fix them. This is, in effect, money in your pocket. Today: front and lateral raises.

Pinkies up

The lateral raise is supposed to engage the distal muscle fiber of the main shoulder muscle—that's the "shoulder cap" furthest away from the body. Most people don't realize that at the top of the range of motion, your pinky finger should be pointed towards the ceiling, not the back of your hand—as if you were pouring out a glass of water. Be sure you're raising the weights about six inches above the point at which your arms are parallel to the floor in order to fully contract the deltoid. —Devan Kline, Burn Boot Camp

Let it flow

When performing a lateral raise, you want your arms to be fully extended, but not locked, as many faithful gymgoers tend to do. Locking your elbows is the equivalent of kinking a hose—the energy stops there, and can't flow freely throughout the body until the kink is removed. Also, be sure that you maintain a straight line from fist to elbow to shoulder throughout the range of motion. —Josh Cox, Anytime Fitness

Brace yourself

Don't arch your back or rock your torso in order to lift the weights during a front raise (or a lat raise). Keep your back straight, and your core engaged. A good way to prevent yourself from cheating is to not worry about going heavy on this exercise. The front raise targets relatively small muscles in your shoulder, so focus on completing between 8 and 12 repetitions with perfect form. —Idalis Velazquez, IV Fitness

Read MoreChiseled Shoulders Can Be Yours With 4 Quick Tweaks

Here's how to fix it.

By Jay Willis

Straighten out

Pay attention to two factors in particular when setting up. First, keep that core engaged by pressing your thighs together, squeezing your butt, and bracing your abs. This will help prevent the torso from bobbing around. Second, it's okay to keep your arms completely straight on front raises. Bending the elbows reduces the tension maintained during the lift, which can in turn strain the connective tissue around the joint. You won't be able to lift as much weight with straight arms, but you'll help strengthen the tissue around biceps and shoulders. —Will Torres, Willspace Personal Training

Jay Willis is a staff writer at GQ covering news, law, and politics. Previously, he was an associate at law firms in Washington, D.C. and Seattle, where his practice focused on consumer financial services and environmental cleanup litigation. He studied social welfare at Berkeley and graduated from Harvard Law School... Read moreRelated Stories for GQFitness