It's easy to think of interior decorating as a low cost minor renovation to your home. Of course everyone thinks they know how to paint, and some do but most do not. There's a lot of little things (knowledge of paint, paint colors, types of wall paint wherever it is acrylic paint or oil paint, brand of paint-preferably Benjamin Moore, ways to apply, etc. etc.)
Paint home – it's a good time to paint interior of your home when you start getting mildewy looking blemishes over the surfaces of your home. I have seen mildew on both inside and outside. And another good reason to paint is when your color starts fading. Peeling paint is even worse than color fade since none one knows really what the color was but they know it should not be peeling.
Wall paint – this is where most people start painting, it gives you the largest bang for the buck when you change the color of a room you have changed the looks of the room. And this is a part of interior decorating because the wall colors greatly affect the rooms atmosphere and can either in hands or take away from the furniture you put in there. And that would be part two of your interior decorating process choosing your furniture.
Interior decorators – if you're at a loss on choosing paint colors for the home interior you might want to consult with a interior decorator, you can show him the home interior and the rooms you would like to paint or decorate and the furnishings that you will be using and they can assist you in selecting the appropriate paint color.
Ultimately – it is your decision since this is your home what to do about your paint colors on your walls and trim and even your ceiling. But sometimes some outside opinions could spur some great ideas that you wish you would've thought of before.