Metabolism is the chemical process of breaking down food to provide energy for basic human functions at complete rest (Basal Metabolic Rate) and physical activity.
You can increase your total metabolism by increasing your physical activity and/or BMR. BMR is mostly dependent on your body size and body composition. You can increase your BMR by increasing your proportion of muscle to fat since muscles use more energy than fat.
General facts:
BMR of women are less than men due to smaller body size and lower proportion of muscle.
BMR decreases with age due to gradual loss of muscle.
BMR can decrease by 20% when your body adapts to starvation to conserve energy (e.g. crash dieting or fasting). In addition, rapid weight loss is accompanied by losing muscle mass leading to a decrease in BMR.
Tip? Use your muscles i.e. do physical activity such as strength training which builds muscles at the same time!
Source:
Mann, J. and Truswell, S., 2012. Essentials of human nutrition. Oxford University Press, New York.