As said I would give complete body workouts a go for a few weeks. These don't have to be farting around as they are thought of. I know some commendable PT's that get their clients doing these due to the harshness on the system if done right. Do it in the style of circuit training to start off with, whilst putting decent effort into every exercise. Do three or four circuits followed by some abs and or core work.

After you have gotten bored of that then you could maybe try a push/pull/legs routine. These also seem to be all the rage at the moment.

if your not comfortable with all the equipment or looking up exercises to do then speak to one of the trainers at the gym you have joined.