Here's my 0.02$.
- Don't try free painting when you are tired, stressed or low on blood sugar.
- I find a rigid rest for my forearm very helpful - I use a broken broom handle, usually I can find a surface to rest it on.
- Use a Good scrupulously clean brush. Wash it, if it starts to 'gunk' up.
- Make sure your paint is perfectly free of old dried paint, dog hair, dust, whatever - filter it, if needed.
- Load only a small amount of paint onto the brush at a time.
- I find it much easier to Push the paint up to a line than to try to Pull the paint next to a line.
For vertical or horizontal lines in the field of a wall, a plumb line in faintest pencil (6H) and a steady hand works faster and better for me than taping (and I am a painting newbie). I also work by hand for vertical surfaces up against trim (door or window frame) and horizontal surfaces out of sight lines (underside of window trim).
I do use the 'frog' tape in the plastic container when I am meeting two different colors (wall v trim) that are in sight lines. I just don't seem to have the requisite skill, experience, whatever, to get perfect looking lines. The frog tape works nicely, but it still takes plenty of time to apply the tape in that nice straight line.
I have had it bleed through when the tape wasn't PERFECTLY adhered in every spot of the line and when I was using a freshly washed brush that still had too much water in it. This thinned the paint and allowed it to creep under the tape where it didn't make sufficient contact.