Well, one good idea is to get a job at places that usually accept a lot of workers, like a McDonald's or a Dairy Queens. If you're a kid, and you can't get a job (like me), then do things like chores, mowing lawns, bake sales, and odd jobs you can find around your neighborhood. Good luck!
In my opinion, you can earn at least $20 a month through setting up a small business. You can decide to start selling candies and other household which you no longer use. This will enable you make even a larger amount than that.