Depending on what you want to keep, you just have to move the files from your existing computer to their corresponding places on the new one. In your Home/Library folder, you may want to keep the Mail & Safari folders, for example. You can move the Home/Pictures and Home/Music folders to keep your iTunes and iPhoto libraries, and so forth. It all depends on what you have and what you want to keep. Just go through the Library, Home/Library, and Home folders and you should find everything you'll need.
If you're having trouble finding any specific files, post here and I'm sure someone can help.