Hiya Kevin, welcome to the forum...
Skill cannot be learned, it is developed. Technique can be learned, but acquiring the proficiency to be called "skilled" is generally a time consuming process...Repetition, mostly...
...I almost got fired from my first painting job, while cutting in a caulk joint on a window frame--The frame was square but the caulk joint was all over the place and trying to keep a straight line was impossible...Thinking back, I don't believe any piece of tape would have made it easier. Painters are required by law to be able to correct the sins of ineptutude committed before us...This includes cutting in a swayback or wavy ceiling...The forgiving thing is that
most people don't see with the scrutiny that a tradesman does--A serious tradesman, anyway...What I'm saying is that the wall-ceiling joint may not be as straight as you thought...I've "straightened" a lot of those out in the last 18 years, you get a "feel" for them after a while...
Don't worry about the straight lines, they will come. You start out as slow as you need to be to do satisfactory work. Pick a room in your house to practice in and paint it 20 or 30 times, you'll find the cut in gets easier AND faster every time you open that can of paint...As the room becomes incrementally
smaller ...
As far as tape goes, use it if you must, but remember that masking tape works on the principle of
pressure; The harder you press, the better it sticks. And yes, it will remove paint if the paint is relatively new or the substrate is not sound...Blue or green low-tack tape is recommended, though a lot more expensive...
Good luck