One of the biggest pain points for people who are doing painting projects on their own is getting crisp clean paint lines when using painter’s masking tape. This is especially troublesome when you have heavily textured walls as the texture makes a tough surface for the tape to create a seal against. There are 2 tricks that can help you out with this:
Use a high-grade painters tape (like FrogTape) that is specially engineered to help prevent paint bleeding. FrogTape has a polymer that reacts with the water in latex paint and instantly gels to form a micro-barrier that seals the edges of the tape, helping to prevent paint bleed. It isn’t a 100% guarantee that you will eliminate all paint bleed, but it certainly helps keep it to a minimum.
The best thing you can do, however, is paint over the edge of the tape first with the color already on the wall. So if your wall is already white, and you are trying to add a blue detail, you would put your painters tape down where you want the transition, and then first paint the edge with the original white color and then let it dry. THEN come back over it and paint with the new blue color, using strokes that pull away from the tape, not towards it. By painting the edge with the original color, it helps create a damming effect at the seam of the original color, which then will result in a perfectly crisp color transition.