All you really need to play poker online is an account at a poker site and some money to play with but to improve your chance of success there are some very helpful things that you may want to look into.
1. Poker Tracker
To start you should definitely purchase a copy of Poker Tracker for about $ 50. This piece of software is one of the most valuable things you can invest in when you decide to take your poker playing a step further. Poker Tracker basically stores all of the hands that you play online so you can look back at how you played at any specific time. This is a very helpful tool for finding flaws in your game. It also provides statistical information about yourself and your opponents which can give you insight into how you and your opponents are playing overall.
2. Poker Ace HUD
Another thing you may want is an add on for Poker Tracker called Poker Ace HUD. Poker Ace shows stats on your opponents while you are playing online. This can give you more insight to how your opponents play and can effect how you play your hand if you know how to use it well. It will cost you around 25 bucks. It is not necessary and you should not rely on it if you ever decide to start playing live poker. Although if you play multiple tables at once I would recommend it because your attention is scattered and you can not focus on individual opponents as easily.
3. Rake back
You should get rake back if possible because it will save you lots of money in the long run. In case you have not heard of rake back it reduces the amount of rake you pay to the poker site by giving you a percentage of your rake back since the name. There are a lot of different websites that offer these programs. Before you sign up at a poker site sign up first because you need to enter a special code when signing up.