Use of Space
If you're painting an inside room, the first consideration is use of space. Again, the type of paint you use should be your first decision, because it may restrict the color palette you'll end up using. Better to narrow those choices down as much as possible before your eyes start to cross at all the samples you'll be looking at.
As with exterior paint, a lot of those choices come down to the chemical makeup of the paint you're using. Still, make sure you know exactly what the space you're painting will be used for: Are you painting a kitchen? Do you have, or plan to have, small children in the house? Do you want a faster cleanup job in bathrooms or areas with a lot of foot traffic? While ultimately your decisions will be about color and aesthetics, knowing where to look first -- for each area you want to paint -- will save you both time and energy, as well as giving you a game plan for how those areas will work together.
For high-traffic areas, something highly durable may be required. A lot of popular finishes these days require enamel paint, for example. By laying out your design plans ahead of time, you can consult a paint professional to make sure that what looks like a matching shade in the store doesn't come out looking odd or out of place once it's on your unique surfaces.