Next, you may need to do some detective work to figure out what's already on your walls. Short of scraping them down -- another level of backbreaking work in an already ambitious project -- knowing what you're working with can help with your decisions.
One of the newest innovations is paint-plus-primer, which implies you don't have to wait before digging into your color choices and getting to work. But this invention is still in its infancy, and you should definitely get the help of your local home improvement store's paint expert for your particular situation.
And then there's the question of integrating styles, if you're not tackling the whole house at once. Say you enjoy one room's existing decor and don't want to change it. It's important to think about how your plans for the hallway just outside might interact: Certain textures and colors may not work well together.
And, most confusing of all: What if you really like a room's existing paint job but want to touch it up? Depending on when your house was built or last painted, you could be in for a lot of detective work. Those leftover buckets and cans in the garage may have changed over time, or the paint on the walls might have faded. Matching existing paint can be a lot more complicated than it seems, and you might end up with a do-over no matter how much you love what's already there.