Hook a band around thumbs and throw it over your head and around your back so the band goes around the outside of your arms. This will help keep your elbows in where they should be. If your elbows flare the band will roll up your neck.
Lay back into position; stomach up, shoulders back and get your swole on! When pressing punch your hands and squeeze your hands through the rep. This keeps stress off your shoulder and pecs and recruits more motor units because there are so many nerve endings in the hands/fingers.
Sets and reps are totally dependent on you and your current training priorities.