Whats the best way to ask to stay at you're friends house?
It's more polite to wait to be asked, but I suppose you could ask her if her parent(s) would let you sleep over sometime.
Explain why you need to stay over and if you cannot respect that opinion
bring over something that required time, say Im having fun, I hope We dont have to leave soon.
I would say in a conversation if they were talking about something at there house, you would say, I have to sleepover sometime. & then they might suggest a date.