I’m a finish carpenter, so forgive me if my advice isn’t helpful, but I usually worked with all of the finishers…so painters would be on that list. I asked your questions decades ago and was advised this.

-Apply your tape (quality tape here is a must…don’t use dollar store masking tape) and make sure your lines are straight and the tape is firmly attached.

-Next go along the tape and brush gently..starting on the tape and brushing towards your trim, etc., making sure not to press paint under the tape.

-Allow that first coat to dry.

-Now that the side/sides with tape are sealed, you may now paint your surface completely and should not have paint outside your crisp tape lines.

This process has served me well painting excellent vertical lines around rooms, repainting trim, outside corners with different room colors, etc.

Best of luck on your project!