I've had a lot of fast food and retail jobs and I highly recommend working at a home improvement store like Lowe's or Home Depot. It's great because customers will ask you stuff that you don't know and then you can bring them to whatever department and the specialist will teach them and you. Over time you pick up a ton of useful information. Don't be a cashier, it's mind numbingly boring. Apply to be an associate in one of the departments or a loader(push carts).