The best way to speed up the metabolism is a regular exercise program and having 6-8 evenly spaced meals a day. Green tea and certain vitamins can help as well.
One way to slightly speed up your metabolism is to drink black coffee. A couple cups a day would be ideal. It does not work that way, however, if you had sugar and/or milk.
You can eat six healthy meals a day, this tends to keep your energy up this way and it will keep your blood sugars stable throughout the day to keep it constant.
Lifting weights (even small amounts) is proven to speed up metabolism for nearly 24 hours after the exercise is completed. To keep your metabolism high, it is important to eat regularly - preferably six small meals a day instead of 3 large ones.