I've never done gym work specifically for MMA before, but do go to the gym a fiar bit (i play rugby). Rather than isolating exercises (i.e bicep curls) look to do compound exercises, then supplement them with the isolation.
The three main are Squats, Deadlifts and Benchpress. These three will give the whole body a general work out. You can then add to these for upper lower body, things like lunges, dumbell flyes, bent over rows, power cleans etc. to supplement to main movements.
As i said, i've never done fight specific training, but these will give you good all round strength in useable areas (i.e going to the gym and bicep curling all day isn't going to help you in the real world, apart from being able to lift a pint to your lips with ease :P )