THIS IS THE WAY. I paint professionally. We tape all trim except the tops and bottoms of windows/ doors where you cant see. We then use white or clear AlexFlex caulk and lay down the thinnest bead possible on the edge of the tape. Then, wipe off most of the caulk or spread it out as thinly as possible. Paint the masked area immediately, and remove the tape immediately after painting to reveal a crisp cut line with no bleeding.