How do I have a nice edge painting a wall by acoustic ceiling, white ceiling and dark blue wall..?
The trick we use is to run what we call a "fat" caulk line around the ceiling. If your ceiling is white use white caulk. Allow the caulk to dry overnight. If you are not comfortable free handing this, try using a pencil to draw a line. This gives your eye a line to follow and should help with the straight line.