How to paint a mural....
Agree what the kids (for whom you are painting the mural), want on their bedroom wall.
WARNING - at this stage the kids will probably want hundreds of cartoon characters, all captured in exact likenesses, and fighting away in some improbable location. Unless you've got a huge wall and a ridiculously large amount of time spare on your hands, it's best to whittle your list down to a few of their favourites.
Do your sketches.
Put paint on the wall until it's done.
(Use of Kirby Krackle is optional)