It's important to remember that you can't spot-tone. Your goal should be to reduce your overall body fat and increase your lean muscle mass. Eventually, the trimming will get to your waist and to your bum. If they're your problem areas, unfortunately, you will see results there last.
A combo of diet and exercise is the best. I know, I know, that sounds so cliche, but it works! Cardio is great, but don't forget to throw in some strength training (if you're tight for time, target bigger muscles like your quads and hamstrings). The cardio will help you work off some fat, while the strength training will boost your metabolism. The latter's important.
Let us know how it goes!