#1 - Short of having a medical condition affecting your thyroid the #1 way to increase your metabolism is to increase Lean Body Mass (LBM).
Around age 30 we begin to see a decrease in muscle mass which in turn decreases our metabolism. Laziness makes us fat, sick and more lazy... the death spiral.
If you are over 40 and have never had your thyroid tested consider asking your medical doctor to test it with a simple blood test. Maintaining proper hormone balances is our key to longevity, productive living and disease prevention.
The medical industry uses the body mass index (BMI) which is very limited and hugely misrepresentative for most individuals. The fat free mass index (FFMI) is a much more accurate representation of the bodies composition.