Last night there was a huge, house-rattling windstorm. This morning, there's a new hairline crack in some ceiling drywall. What's the best way to repair it? Should I fill the crack with spackle first, or can I just paint it straight away?
Consider using a paintable latex caulk. Apply a very small amount then work it into the length of the crack with a finger. Wipe off all excess with a damp rag or sponge, then paint. It is a good method requiring no sanding. If your ceiling is painted with flat (no gloss) paint, as most are, you will not be able to see it when you are done.
The only correct way to fix it, IMHO, is to get some paper drywall tape, and embed it in some setting-type (the powdered kind that you mix with water yourself) compound. Do not use the pre-mixed, and do not use fiberglass drywall tape. In my experience, any other method will eventually open-up on you.