Heavy incline barbell presses are a well-known chest-builder, but they can be dangerous if you are training alone. Done in the Smith machine, they will hit your upper pecs through a full range of motion with less risk of injury. You can work in some partials to train weaker parts of the movement. Finish off with a set of incline presses with a huge drop set, removing plates and getting right back under the bar each time you hit failure. This technique flushes the muscle with blood and takes you well past failure. Partials and drops on the incline Smith should help your chest a great deal.
Forced reps with a partner is a good technique to use for new growth, as it gives the muscle more stimulus after the mind and the muscle is disconnect and you are physically unable to complete any more reps without help. Using the bench press as an example, load the bar with a slightly heavier weight than you might use when training alone. Aim for got your target number of reps on your own, even if you know you may fall short by one or two reps. If you are going for 10 reps for example, and fail at 8, you can use forced reps to complete the set. Have your partner hold the bar lightly on the descent, then help your power it back up to the top, offering only as much help as necessary for you to complete the rep. This is where a good training partner comes in handy. You want someone who is familiar with your limits and who can safely help through the set.