How to paint a straight line at the ceiling like a pro without using any tape. Paint your ceiling first, wrapping the corner. Take your ubiquitous 5-in-1's back edge and gently score a mark. Just use the corner as the naturally flowing guide. Using a 3 inch brush loaded with paint, just cover the line.
ALWAYS USE A BONDING PRIMER. Not primer for wallpaper. Not primer for fresh drywall. Not paint and primer combined. Somewhere on the instructions or label, the can should say something like this " will adhere to glossy surfaces"