Some good advice (except for the "FL isn't the place to ask about planted tanks." We aren't the
only place, but we've got plenty of knowledgeable members

)
First of all, two questions that we need to know the answers to before we can really go into depth.
#1, how much light do you have going into the tank? If you aren't sure of the wattage of your lights, tell us the length and type of bulb (standard fluorescent is my guess), and we can look it up. Divide watts by 55 (the number of gallons in your tank) and you've got wpg, which was alluded to above. The more I study lighting, the more I realize that this concept is about as concrete as the "one inch per gallon" guideline for fish. That's to say, it isn't concrete at all. Different types of fluorescent lights have different levels of efficiency, and halogen and incandescent bulbs are entirely different, so watts per gallon is only so useful. Still, it's a good starting point.
#2, what kind of substrate do you have? Gravel, sand, etc...
If you have plain gravel, this will make rooted plants more difficult, but not impossible, to keep.
You can also gently remove as much of the gravel as possible and replace it with Eco-Complete, which is ready to add to a tank straight from the bag (no rinsing required).
Even with a low-light, gravel-substrate tank, there are options. My two favorites are Java fern and Java moss (and its relatives). These plants are tied to either rocks or driftwood (there's a fake rock made specifically for rooting things like Java fern), rather than planted in the substrate. They require little light, no added CO2, and make beautiful additions to nearly any tank.