The first this you need to worry about is the temperature. The "normal" temperature you need for the water is 25-27'C so in winter you need to have heater inside the tank. Some fish need it cooler some fish need it hotter you need to research a little for the fish you want to keep. If the water is cold the fish will have slow metabolism (slow move, not active so much) and the warmer you keep the water, they faster grow and they're more active.
The n.1 thing for your aquarium and too keep the fish happy and active is the water maintenance. From my experience the best thing for the aquarium and fish is to change 15-20% water level every 7-10 days. That way the water will stay fresh, Ph will be normal and the ammonia in your tank will be lower. Also in every pet shop have chemicals for the water quality so you can check that out and ask the dealer for more information.
Now something for the fish. Do NOT overfeed your fish. No matter how many times or how much you feed them, they always eat. I feed my fish 2 times a day with the same amount of food. Don't think that if you feed too much they will grow faster, you will overfeed them and that may cause death to fish.
Stay tuned for part 3.