Inform them where the sleepover will be occurring. For parents, it's all about information. The more they have, the more comfortable they will feel with allowing you to go. Start by telling them whose house you'd like to sleepover at.

Tell them who and how many people will be there, whether it's a big party or just a few friends. Tell them if it's going to be boys and girls or simply one sex.

Keep them informed on what you will be doing at the sleepover. For instance, maybe you are going to a dance, and then back to a friend's to watch a movie and then you're going to crash there. Having a game plan will ease their mind that you will not be getting into mischief.

Encourage them to call the parents at the house where you want to stay over. Give them the contact information and let them call. This way they can have a conversation and ask any questions to the people who will be chaperoning.

Offer for them to hang out for a half hour or so when they drop you off. If they are still slightly uncomfortable, tell them they can drop you off and then meet the people of whose house you will be at. While it's a bit of a drag to have them around, 30 minutes at the start of the night is better than not being able to go at all.

Give them a task to do for the sleepover. For instance, if this is a surprise party, tell them that you're supposed to make cupcakes. They'll be so worried about the cupcakes, they won't even realize that the sleepover is something you were asking about.

Prove to them that you are responsible. If they initially say "no," accept that answer without a fight (you don't want to irritate them). Then ask to let you prove to them that you are responsible, prior to the party. Getting in a negotiation often leads to something that both parties want.