From Yahoo Health:

The main points -

Don't eat less than 1000 calories
Eat every 4 to 5 hours
Make breakfast a priority
Protein with every meal
Aerobic exercise 4 to 5 times per week
Strength training 2 to 3 days per week

I like this type of advice - simple, and to the point. 

Especially as the focus is ON metabolism, as this is overlooked by a lot of people. 

As you get older the natural metabolism CHANGES - and changes greatly.  Slows down, and it can be quite unexpected.  I went from eating, drinking, scarfing, pretty much anything I wanted - and staying skinny.  And I had (have) quite a sweet tooth, but it didn't affect my weight.  And then over the course of six months, at 31 - I put on 15 pounds.  And now, I go back and forth, battling that extra 15 pounds, depending on how my eating habits hold up (or don't).

Getting the metabolism up, in a healthy, simple way, has been one of the best ways to automatically fight weight gain.