Cancel the gym membership and join a local bootcamp?
Otherwise you need a good balance of cardio and strength work. Interval training when using cardio equipment is best, they normally have interval training settings on the treadmills/ski machines etc.
Half hour cardio training, half hour strength, do 2 x 20 reps with a 30 second break between each set.
Classes are good too. I find I get more out of classes than just going to the gym because I push myself more.
wouldn't you get bored following a set routine though? you could try downloading the workouts for something like p90x or p00lean and there is lots of variety there if you want a very structured approach
agree about classes, am doing a 30 class challenge which means trying almost 10 different classes a week and some are surprisingly tough
I have to have new stuff to do or try though, I couldn't cope with the same workout every day
