Primer is your friend.
Use better tools. Get a 2" tapered cutin brush, I like Purdy brand---the brush should be recommended for the type of paint being used---the dust cover on the brush will tell that.
Use the smaller 1" diameter rollers, you will get better coverage and no roller lines as both ends of those rollers are tapered.
The secret to even paint jobs with a roller is to cut in the edges/corners and keeping a 'wet edge'. That simply means using the brush to paint a 1" or 2" border at the taped or trim areas and in corners. Then use the roller to paint from the top to the bottom of the wall in bands about 2 feet wide. Apply the paint to the entire band and then run the roller in one direction and move over to do the same thing. Once that is done, do not touch or reroll that section again. Move across the wall that way and you will easily cover and blend the bands.