Grip. Hold the bar in the base of your palm, close to your wrist. Squeeze the bar.
Grip Width. Hands inside the ring marks of the bar. Vertical forearms at the bottom.
Thumbs. Wrap your thumbs around the bar. Don’t Bench Press with a thumbless grip.
Wrists. Straight line bar to wrist to elbow. Don’t Bench with bent wrists or they’ll hurt.
Elbows. About 75° out at the bottom. They shouldn’t touch your torso or flare out 90°.
Forearms. Vertical to the floor from every angle: from the side as well as from the front.
Shoulders. Keep them back, on the bench. Don’t shrug your shoulders forward at the top.
Upper-back. Squeeze your shoulder-blades together to increase stability when you Bench.
Chest. Raise it to the ceiling. Reach to the bar while you lower it. But keep your butt on bench.
Head. Setup with your eyes under the bar. Keep your head neutral. Don’t push it into your bench.
Lower Back. Natural arch. I should be able to slide my flat hand between the bench and your back.
Butt. Keep your butt on your bench when you bench. Don’t cheat by raising your butt off the bench.
Feet. Flat on the floor, not in the air. Feet under knees. Use a shoulder-width stance like on Squats.
Unracking. Unrack the weight by straightening your arms. Move the bar above your shoulder joint.
Way Down. Lower the bar to your mid-chest. Tuck your elbows in 75° while you lower the weight.
Bottom. Straight wrists, vertical forearms. Elbows in but not against your torso. Bar on mid-chest.
Way Up. Don’t pause at the bottom. Press the bar back to above your shoulders. Lock your elbows.
Lockout. Lock the bar over your shoulder joint. Lock your elbows at the top. Don’t bend them back.
Racking. Lockout with straight elbows. Move the bar back against the rack. Lower it in the uprights.
Bar Path. Diagonal line from your mid-chest to shoulders. Not vertical over shoulders, neck or chest.
Breathing. Big breath at the top, hold it on the way down, hold it at the bottom, exhale at the top.
http://stronglifts.com/bench-press/