The most important decisions a gamer makes is what platform to use, and which games to buy. While no platform is the best for all gamers, there is usually a platform that will be right for you, depending on what your tastes are for gaming. For example, if you enjoy MMORPGs, your should usually get a high-end gaming card and play games on a PC. On the other hand, those who like first person shooters will be better off getting something like playstation. If you aren't sure what types of games you enjoy, play both types at conventions or by using the platforms your friends or family may have.
The games you buy are equally important. To avoid sinking money into games you ultimately end up not playing, I recommend borrowing or renting games before you make a purchase. Borrowing games is best if you have friends who are gamer, as this will cost you nothing. But if this isn't an option for you, you can rent games at a kiosk or by obtaining a membership at Gamefly, the premiere online game rental site. As of this writing, they will allow you to get a free trial that lasts a full month.
Another thing you can do to save a bit of money is to buy used games. You can find them online and as long as you aren't buying new releases, you should have no problem finding the game title you are interested in.