The push-up looks basic and is anything but. Done right it is a moving plank that trains chest, triceps, and abs together; done wrong it is mostly shrugging and sagging hips. Two cues fix most of it: one straight line, elbows at 45 degrees.
Set your body in one straight line
Place your hands slightly wider than your shoulders, fingers spread, middle fingers pointing forward. Straighten into a plank: ears, shoulders, hips, and ankles in one line, abs braced, glutes tight.
Push the floor away slightly to spread your shoulder blades before the first rep. Keep your neck long and look at the floor about a foot ahead of your hands, not at your toes.
Lower with elbows at 45 degrees
Bend the elbows so they travel back at about 45 degrees from your ribs instead of flaring out to the sides. Take two seconds down, with the body moving as one rigid piece from head to heels.
Lower until your chest is a fist's height from the floor or lightly touches it. Your head stays in line with the spine; leading with the chin fakes depth that your chest never reached. Spread your fingers and grip the floor; active hands make the wrists happier and the whole rep steadier.
Touch, then press the floor away
At the bottom, press the floor down and slightly back until your arms are straight again. Keep the plank line the whole way — the rep ends when the elbows lock softly, shoulders still away from your ears.
Breathe in on the way down and out on the press. If your hips rise or your belly drops before your arms finish, the set is over; grinding half-plank reps teaches the wrong pattern.
Fix the two classic failures
Sagging hips mean the core lost the plank. Squeeze glutes and abs hard, and if it happens again, drop to an easier version right away instead of grinding ugly reps.
Piking — hips high while the chest barely moves — means the load is too heavy for your current strength. The fix is not more effort; it is an easier variation, and that is where most people quit too early.
Use regressions, then progress
Start with incline push-ups on a counter or bench, or knee push-ups, at a height where ten clean reps are possible. As sets get easy, lower the incline or move up to the toes.
Log reps and incline height in Bulky and chase small steps: more reps first, then a lower surface, then full sets on the floor. That ladder takes most people from zero to solid push-ups within a couple of months.