Started casually selling when I was roughly 18 years old to get rid of things I no longer needed/wanted. Still doing that over a decade later, just more auctions.
Payment policy
PayPal. Gotten burned too many times by checks and phony money orders.
Delivery information
USPS. Usually Priority Mail, although I list all auctions as Parcel Post, if I can ship it faster for the same or slightly higher price, I'll do it.
Return policy
No returns, sorry :( Too many bad dealings with ill intentioned bidders.