Lifting weights is only a part of the equation to health and fitness. Nutrition and sleep are the other main components. Nutrition will need to be adjusted according to your goals. If you want to maintain your current body composition your diet only needs to be altered if you are not meeting that goal. If you want to gain muscle you will have to consume an extra 500 calories a day. Typically a pound of weight gain, muscle or fat, is equal to 3,500 calories. If you goal is to gain muscle then you will have to eat 500 more calories a day with a higher concentration of protein. The intake recommendations for protein intake for muscle gain are constantly debated. Generally between 0.8 and 1.2 grams of protein per pound of lean body mass is adequate. It is important to use lean body mass rather than total body weight because you do not need protein to maintain body fat stores.
The type of program followed will matter also. If the program has many sets, is a circuit, or involves days of aerobic training than you may have to increase you carbohydrate intake to match your energy needs. Carbohydrate can be consumed at 4-7 grams per pound of lean body mass. From this point you can alter the intake to balance energy need and weight gain/loss. Start with general guidelines and then modulate your meals to your needs.