A lot depends on your lighting. If you look in typical plant areas of forums you will find lots of talk about WPG. What they mean is watts of fluorescent lighting per gallon of water. The idea is that as a tank gets bigger, it needs more light to have enough for a particular plant. The values sort of work as long as you are looking at a tank between about 20 and 75 gallons. If you go to a smaller tank, it takes a higher WPG number to have the same result and at very large tanks it takes a little less to get the same result. Many of the more common plants are called low or medium light plants. What they are talking about for low is maybe 1 WPG and medium would be closer to 1 1/2 to 2 WPG. For low light you should be looking at anubias, java fern, java moss and similar plants. At the low end of medium light you can get away with valisneria, amazon swords, hornwort and the like. In general, plants with colored leaves like reds and such require more light than green plants. Your best choice if you are going to go to plants is to go to the planted tank section and get some help there. I am far from a plant expert but thought I could at least give you an idea of the light terminology you will see.
The best advice I think I ever got was to buy whatever is cheapest. The idea is that they are cheap because they are easy to grow. The hard to grow plants end up costing more to produce so you pay more for them.
