First, gather all of the things that you don't want anymore and have some type of value. Or you can look anywhere from stores to other people selling things.
Step2
Find people that you think would want to buy any of these items. Say positive things about the item and if they ask you how much you bought it for always tell them something more than you're selling it to them for.
Step3
If they say that they're not interested, pressure them, but not too much to make them feel uncomfortable.
Tips & Warnings
If at first you don't succeed, try, try, try again.
If you know that a certain person likes certain things, try to sell them something related to that.
When you pressure someone, be careful not to overdo it.
If you are a kid at school, make sure a teacher doesn't catch you.
Novice 
