One of the bulletproof ways to boost your metabolism is to increase muscle mass because the more muscles you have the faster your metabolism.
This is slightly easier said than done because it means you need more physical activity to maintain the same weight. In order to burn additional 100 calories per day you will need to increase your muscle mass by 3 to 5 pounds.
In order to do this, increase the amount of time you devote to working out every week. Increase the weight you lift, and run and cycle for a few minutes longer to get rid of additional several hundred calories.
In addition to working out more, there is also the issue of eating smaller meals more often and getting more sleep. The latter is definitely the easiest and the most enjoyable activity, but the bottom line is that more effort is necessary after the age of 30 to maintain the same figure.