Lots of good advice here, but the simple answer is interval training. If you have one fast group ride a week, you should have one or 2 other rides that consist of very hard intervals..then a few very easy recovery rides the day after the hard rides. If you're thinking of it in terms of effort out of ten, the riding a lot at a 7-8 effort will not make you as fast as riding the same amount, but splitting it between efforts of 9-10 and 3-4. This kind of work conditions your cardio vascular system better, and will burn more fat, losing weight.