First, you must enough enough CO2 to support so many plants. Sufficient CO2 levels can be derived from many small fish or a few big ones and/or CO2 injection devices.
Second, you should have good lighting -- for a 55 gal tank -- probably need atleast 120 watts of compact flourescent lighting running 8 hrs per day.
Third, you must have good substrate - not just glass marbles or gravel. I use Flourite in my planted 75 gal tank -- works well and supplies nutrients to the plant roots.
You'll find some plants do well, some don't. I have hundreds of little snails in my tank, and although some people think they are a nuissance, the help keep algae from growing on the leaves, not to mention the glass and other rocks and ornaments I have in their. Good luck with you planted tank.