Mix all your cans of finish paint for consistent color

Because I use a fast-drying primer, I can apply the finish coats almost immediately. For the room,
I gave the ceiling one coat of white finish paint, and the walls two coats.
For the finish coat, I roll the ceiling first so that any drips or spatter that I get on the walls will be covered with their finish coat. When cutting in the ceiling, I again overlap the finish paint slightly onto the walls.
It's still not necessary to be extremely tidy; I just try not to leave any globs of paint on the walls.
Next is the final coat on the walls, and I don't want to be short on paint. I also want a little paint left over in case I need to touch up or repair a wall in the future. But custom-mixed colors usually vary from can to can, which can be obvious if I have to buy an extra quart to finish a job.
The trick is to overbuy and then mix all the cans of paint together thoroughly before I start. Most paints cover around 400-sq. ft. of flat surface per 3.78 litre.
I've seen painters pour half of a gallon can into a container and then pour half of a second can into the first. They continue this process around until all the cans have been blended completely. Mixing paint in this manner is known as boxing, but I find it easier just to pour all the paint into a 5-gal. Bucket.

Be finicky on the final cut in

The time has finally arrived to take the extra effort to cut in neatly. I start at the ceiling line of one wall and cut it in as neatly as possible. It's still okay if it's not absolutely perfect; I'll fine-tune the line on the final coat.
Again, I create the first horizontal line with a high quality 3-in. brush turned on edge. I then complete the band using the full 3-in. width. I also overlap onto the trim slightly, but I don't go crazy. For the project featured here, the trim was to be white, which wouldn't cover the teal wall paint well.

A paint pan minimizes ropes

Instead of working out of a 5-gal. Bucket, I use a roller pan for the finish coats on both the ceiling and walls. Loading the roller out of a paint pan gives me better control over ropes and drips. When filling a roller pan, I pour in just enough paint to fill the deep end of the pan. And again, I don't let the entire roller submerge in the paint. When the roller is saturated, I give it a light twirl to spin off excess paint from the ends.
Roll the walls the same way I did on the primer coat, working in 3-ft. squares and making sure the paint is applied evenly. When the first coat is dry, I go over the walls with light sandpaper using a work light to illuminate lumps or debris that might need to be smoothed out.
Cutting in the second coat gives me the chance to fine-tune the line between the ceiling and walls. Working in an older home, I often find myself having to invent a straight line because the corners are uneven. I take my time and fill in any small gaps left from the first coat.
Don't use masking tape to create a straight corner line, which can make an even bigger mess than you're trying to prevent. Instead, take your time and trust yourself with the brush. You can't do any damage that can't be easily fixed with either wall or ceiling paint.
The roller pad I used for the first coat still had plenty of life in it after one coat, so I didn't want to throw it out. But I couldn't let it sit out overnight either, so I stuck it in the fringe. I just double-wrapped the roller pad {still on the frame} in old plastic grocery bags and set it next to the eggs and milk. Paint dries slowly at refrigerator temperatures. The next day, I let the roller come to room temperature and was ready to roll the next coat.
When I'm finished with the final coat, I use the curved part of a painter's 5-in-1 tool to scrape most of the residual paint out of the roller, and then I throw the roller pad away.
There are gadgets on the market that are supposed to help with cleaning rollers. But cleaning a roller pad can shorten its limited life span and can even destroy a cheaper pad that has a cardboard core.
Throwing pads away may not be frugal, but besides being a pain, cleaning roller pads is inefficient. Every time I try cleaning a pad, there always seems to be a bit of residual paint that spoils whatever I try to paint next.
To store leftover paint, I secure the lid and store the can upside down. The next time I need it, the tint that settles to the bottom naturally mixes back into the paint.