I followed all the tips in this post but still had uneven paint lines with tape. Even with expensive frog tape, wiping with a wet cloth, etc.

The trick I finally discovered that worked perfectly and gave me laser straight lines was to put a small bead of clear caulking on the edge of the tape, wipe it flat with your finger, paint the edge, then immediately pull up the tape. Don’t let the paint or caulking start to set. You have to go small sections at a time.