Things to think about are:
Substrate - get a good one, one that is designed to grow plants, have a
look here for types, would suggest something like the tetraplant or aquabases both very good and shouldn't break the bank, should give the plants something to grow in without getting into the really high end substrates like ADA aqua soil or eco-complete.
Next is lighting - have a read of the pinned lighting article, but basically you have two choices, low light or high light tank.
Low light tanks - less cost, easier to run, less algae issues, 'better/easier' for the beginner, can grow most plants but some more demanding one will struggle.
High light tanks - can be expensive, need to dose ferts daily, but can grow pretty much anything you like and get green carpets on the bottom of the tank, more maintenance required and pruning of the plants, can create stunning scapes pretty quickly.
Tank - bigger is better something in the region of 20-30G would be perfect, big enough to be more stable than small tanks but not to big as to be unmanageable.
Plants - the
pinned plant list has a list of easier plants, take your pick!
CO2 - If you're going for the low light (say below 2WPG (watts per gallon) on a 20G tank) then I would perhaps not think about CO2 yet, you'll have enough to think about without CO2, get it all going and get used to water changes etc then think about adding CO2. If however you want a high light tank, CO2 is a must.
HTH
Sam