How do I set up a tank for plants?

First, decide what kind of planted tank you want. Basically, you have three choices:

1) Low light. If you just want to add a few plants to an existing tank, and don't want to spend money on special lighting or substrate, this is for you.

2) Moderate light. This is probably the best choice for a beginner who's serious about underwater gardening, and is willing to put some time, money, and effort into it.

3) High light. A high-light tank will let you grow just about anything you want, but it's more work and more money. It can be difficult, at least for a beginner.

SETTING UP A LOW-LIGHT TANK

No special setup is needed. The important thing is to choose low-light plants: Anubias, java fern, java moss, maybe African fern (Bolbitis). These plants don't need special care or extra lighting, so this is an easy, inexpensive, and low-maintenance choice. I kept a low-light tank with a mix of plastic plants and low-light live ones for years, and it looked very nice.

SETTING UP A MODERATE-LIGHT TANK

For a moderate-light tank, you should invest in extra lighting and an enriched substrate. The easiest way to upgrade your lighting is to buy a hood with a twin-tube light strip: two flourescent bulbs that run the length of the tank. The easiest substrate is Seachem's Flourite. Unless you have a very large tank, Flourite is worth the money, especially for a beginner.

A moderate-light tank may need some fertilizer. Often, regular water changes and a liquid iron additive is all you need.

The tank should be planted thickly. Make sure at least 75% of the tank is planted. Having lots of plants will out-compete the algae that the extra lighting may otherwise encourage.

SETTING UP A HIGH-LIGHT TANK

If you have 3 watts per gallon or more, you have to inject CO2. It's not optional. If you're not willing to mess with CO2, stick to moderate light.

Even with CO2, don't go overboard with light. Try to stay below 4 watts per gallon, at least if you are a beginner.

Lighting can be anything from metal halide pendants to power compact flourescents to shop lights. Shop lights can be bought at Home Depot very inexpensively, and work very well.

As with a moderate light tank, an enriched substrate such as Flourite is recommended. If the tank is very large, and you can't afford Flourite, pool sand and laterite can be used. Mix the laterite into one inch of sand, then cover with 2" or more of plain sand.

For a high-light tank, a complete fertilizer such as Tropica Mastergrow or Seachem Flourish is a must. You may need substrate fertilizers, such as Flourish Tabs and Jobe's spikes as well.

For a great step-by-step guide to setting up a high-light planted tank, see this article by Chuck.