My experience
From my experience I started with standard gravel, the plants didn't do so good so I switched to Flourite which was great for the plants, but was a friggin mess to swap out, because it's clay gravel and will basically look like a mud puddle if you are not careful. I obviously wasn't. I stressed out all night and thankfully all the fish made it as I only had one tank.
If you have fish already in there then you can do one of two things. Take them out bag them up and switch out the gravel taking care to keep the mud puddle thing to a minimum. BEFORE doing that, research on what types of plants you want to have, then look at their requirements. Like high lighting or low lighting requirements. Then look at their requirements for nutrients, I.E. Iron etc.
Once doing all of that then you can look at the maker or Flourite's website where they list the percentage of nutrients provided by the gravel.
Lighting is done by taking the tanks capacity and getting a light that will offer 3 times the capacity in watts. So if you have a 30 long you should have 60 watts of light over the tank. You might be able to get away with a little less since the tank is not that deep, if it is deep then you need to up the wattage.
If you don't go the gravel exchange route then you'll need to add the nutrients to the water every so often.
The key to keeping plants is to keep the nutrients balanced and have the proper lighting.