It's not my strongsuit either so I'm not really in a position to give advice but over the past few months I've gained close to 10kg on my bench press and the only thing I done differently over that time period was added isometric press ups to my routine. It's a fantastic exercise and you can do it pretty much anywhere.
Just have a stopwatch handy, and go into a press up position. Do a press up, but when you're in the final phase of lowering your body to the floor stop there and hold it. You should look like the
middle dude on this image (although hopefully your nose isn't quite so big).
Now hold that for about 60 seconds (or more if you're comfortable!). It's a truly brutal calisthenic. After about 90 seconds the circulation to your arms starts to weaken and it gets to a stage where you're holding yourself up on willpower alone.
Just try to start doing them more often - it worked for me!
(also, everybody reading this should go and try them right now!)