It is important to have a well balanced workout combining cardio and strength training. Cardio at least 5 days a week with strenght training 3 days a week.
I suggest cardio intervals which means short quick bursts increasing your speed and intensity for a short period of time. Intervals have been proven to jump start the fat burn for max. effect. Also try something new and take in a cardio class at your gym, classes can be the best way to learn exercises and get motivated.