Great instruction from “SparksPeople” regarding proper form for a Chest Press using a Bar Bell:
Bench Press with Barbell
Lie back on bench. Your feet should be either flat on the floor, flat on a foot rest, or up in the air to protect your lower back from injury. Hold a weighted barbell with arms straight up toward the ceiling.
INHALE: Allow elbows to bend to 90 degrees, lowering the barbell down toward your chest (but not touching it). EXHALE: Extend the arms, pushing the weight back up to the starting position. Don’t lock elbows completely.
Keep spine in a neutral position. Don’t lift head off the bench during exercise.