A newly-set up tank will need to have a culture of algae to start algal growth. You can easily purchase them in local pet stores.  Once established, the best and natural way to promote algal growth is to turn on the lights.  In some pet stores, aquarium lights are left on for about 16 hours.  In your home, 10-12 hours would suffice.  Natural sun is certainly the best light source, but it would only cause excessive algal growth.  Keep your tank from direct sunlight, as much as possible.  Heat is also beneficial.  Keep your tank up to 77 ^™F.  This way, you promote growth but still moderate the rate in which algae would grow in your tank.

Do not do too much water changing.  About 10% of every other day or 25% water change a week is ideal to help promote but control algal growth.  Changing too much water disrupts the nitrogen cycle of your tank, and also alters the pH of your water.  Nitrogen-phosphorus balance as well as pH level is highly essential for algal growth and for your fish to thrive.

You must, however, clean up excessive algal growth.  Scrape the tank every now and then to minimize the unsightly proliferation of algae.  Do not use chemicals such as copper to control them.  These chemicals do more harm in your fish and plants.  If you still think that the amount of algae in your tank is not good enough for your herbivore population, it is advised that you farm algae in a separate tank using stones that you can transfer from one tank to another.

So stay tuned.