Recommendations
For players who are on the fence as to whether or not they should start playing poker online, there are a few questions you should ask yourself. First, is whether or not you know when to quit. The first thing I tell anyone who asks me whether or not they should give online poker a try is whether or not they know when to stop. You must have heard countless stories of people who have had their lives ruined due to gambling. I want to make it perfectly clear that this does happen, on a daily basis in fact, and if you are going to play poker online, you need to be very smart about the way you choose to play. The best way to do this is set a losing budget for the day/week/month. This amount should be something you can afford to lose without it affecting your day to day life.
Consider this money as a recreational expense for the month. This way, anything you win is just a bonus, and whatever you lose is simply money spent on a recreational activity (just like going to the movies). If you play this way, not only will you save yourself a great deal of trouble from falling into "the gambling hole" but also be able to have much more fun, and be able to continue your online play for longer than you would otherwise.
Starting out
Find low stakes games that you can start taking part in. Begin feeling out the atmosphere and the environment but most of all don't be afraid to start. There are many sites that offer low stakes games for beginners to get started, and provide valuable experience that users can put to use over time to improve their games. I strongly recommend all people interested in poker to try playing online. Minimum payments to play are very cheap, and since you are playing against other novice players, the chances of winning are considerably higher.
Advanced Players
Play tournaments. I cannot make this much clearer. There are some great tournament sites out there that offer excellent tournament play. Tournaments are the places where real money can be won, and also you will be able to improve and hone your skills that much more because you will be playing against a group of players that are also more experienced. You can take the skills that you can away from the online table and utilize them in real life as well. There are many players who over time become good enough that they can obtain full time incomes from playing online. Though I don't recommend quitting your day job right now, becoming a professional poker player has been a long time dream of many players, and it playing online makes it much more possible for this dream to become a reality.