In reply to Mountain Spirit:
Because of the shoulder pain, you need to start at a level that isn't going to make things worse, which means simple body-weight exercises may be out. The trick is to train at levels below those causing pain, even if it seems the resistance is absurdly light for a while. This seems to be one of the keys to rehabbing injuries.
There are two types of pressing motions: in the first, your elbows are down and your hands are relatively low---the dividing line between pulling and pressing is when your hands are at about armpit level. In the second, you elbows (or often just one elbow) are up, your palm is on the hold, and you are in a manteling position.
The best way to gradually train the first type of pressing is with a lat pull-down machine. Begin with the bar at chin level and press it all the way down to mid-thigh.
Gradually training manteling is harder. Dips are the obvious choice and what you want to head for, but they may be too hard on your shoulders at first if you are already experiencing pain. Knee pushups might be a start, but the biomechanics are not specific enough. Assisted dips are the way to go if you can set it up---standing on a loop of surgical latex tubing to take off body weight works very well but you have to get the tubing and put up with the comments you'll get in the gym. (Don't actually stand on the tubing; use a foot loop.) You start with a really tight loop and make it longer as you get stronger. Latex surgical tubing can be purchased from diving supply stores; get the thickest wall you can find, and make sure it is latex, nothing else stretches like it without breaking. If you have a home gym, you can set up a pulley counterweight to effectively reduce your body weight, as is now common for hangboard workouts.
