The problem: Your butt rises
Push-ups are a great ab exercise, but this is a clear indication that you're not engaging your core.
The fix: Engage your glute muscles by squeezing the cheeks together. This will help lower your butt and raise your lower back.
The problem: Your back looks more like a hammock and less like a board
Your body should form a straight line from your shoulders to your heels.
The fix: Raise your low back toward the ceiling while simultaneously tilting your pelvic bones in the direction of your upper body.
The problem: Improper arm placement
Lots of people place their hands too far forward, which puts strain on the shoulder joints, making it difficult to comfortably engage the buttocks, low back, and abdominal area.
The fix: Your arms need to be straight up and down like a pillar holding up a building, allowing the bones in both arms to better support the weight of your body.
The problem: Poor head alignment
This happens when the chin and jaw are too close to your chest during the exercise.
The fix: Try to imagine a grapefruit-size space between your chin and upper chest, which will align your spine and relieve pressure from your neck muscles.
The problem: Dead legs
Most people think that their legs are just along for the ride. Not true.
The fix: To achieve more muscle recruitment and better alignment during a push-up, it's important to push the backs of your knees toward the ceiling and your heels toward the floor, while flexing your quadriceps ever so slightly.
The problem: You're holding your breath
This one is obvious, but quite often the most overlooked. It's difficult to do anything well while holding your breath.
The fix: Don't force it—just make sure you're exhaling on the way up and inhaling on the way down like you would breath naturally. No yoga-style exhales here.
The problem: You're only doing half a push-up
Far too often people don't go low enough or high enough, but you can't improve or get stronger doing a half push-up.
The fix: Try to straighten your arms at the top of every push-up and be conscious that your upper arms/triceps are at least parallel to the floor at the bottom, creating a 90-degree angle with your elbows.
For more from Tony Horton, check out tonyhortonlife.com