Your body should be a straight line from head to heels. Squeeze your glutes and brace your core to prevent your hips from sagging.
can you currently do in a single set without stopping? Do More Pushups: Maximum Pushup Workout Guide
Chest should nearly touch the floor, and arms should lock out fully at the top. 2. The Strategy: "Greasing the Groove" Your body should be a straight line from head to heels