Your basal metabolic rate determines how many calories you burn per day by just maintaining body temperature and organ functionality. This value must be added to the calories burnt through cardio in order to calculate your total daily energy expenditure. If you want to lose body fat, there are several ways to tweak your metabolism outside of the gym.
One basic way to keep your metabolism high is to eat several small meals at regular intervals throughout the day. Ideally you should eat 5-6 meals spaced 2-3 hours apart. The reason for doing this is that it keeps your energy and insulin levels steady, which means your body will be less prone to storing fat than if you eat say only two big meals during the day.
Daily cardio is an excellent way of maintaining a higher metabolic rate throughout the day. For 24 hours after any intense cardio your body will burn significantly more calories than on a day without cardio. If you work intensely enough it is even possible to double the amount of calories burnt during the actual exercise. For instance if you burn 400 calories during 45 minutes of cardio (depending on your weight), you will burn another 400 calories over the coming day as a result of an increased metabolic rate, giving you a total benefit of 800 calories.
Some studies have found that coffee will increase your metabolism, so this may be worth adding to your diet. However, these effects are minor compared to those gained through regular cardio and a balanced diet. Also, the benefits of coffee are outweighed by the negative impact of the fat contained in the milk of frothy cappuccinos.
A highly effective way of permanently increasing metabolism is to gain muscle mass. Muscle cells require more energy than fat cells to survive. This means that gaining a few pounds in lean muscle weight will create a positive feedback with keeping your body fat percentage low.
If you want to increase your metabolism you must avoid consuming alcohol, sugar, fried and processed foods. This of course removes a lot of what makes life worth living, but sacrifices must be made.
Sleep is another important factor in maintaining a healthy metabolism. If you get insufficient sleep your metabolism will be slower the next day and you will be hungrier than normal and crave sweet foods.