[header] How to throw the best slumber party [title] Ask your parents for permission. [step] It'd be disappointing to get all hyped up only to have your parents say no. Try be extra good around the house and not to ask multiple times as it doesn't help them make the decision you want them to. 
[substeps] Don't make a scene if your parents don't agree straight away. They may need time to think about it and if you throw a tantrum, that'll color their view negatively.