I work hard i do 3 days a week in my LFS and i do 3 days at college, i like to use my one day off to relax by watching my fish and maintianing them, i save my money and if theres a fish i want ill buy it, ive earnt my money, that and buying more songs for guitar hero and rockband!
First, I frequent my lfs so that I know approximately how much to save. Then I save for about double the cost of whatever I want. That way, when I do buy a fish, I have money left over and I stick that in a jar/box/sock for next time. It takes a lot of patience, but it's worked so far. That extra money can also be used for emergencies.