If you have an entire house to decorate, it can seem like a daunting prospect but you can tackle one room at a time, one element at a time. Start with the basics of lighting, color, flooring then add in key pieces of furniture and soft furnishings before finishing with some great accessories.
It can seem easiest to decide on a theme in the beginning and to stick with that theme as you make your decorating decisions. For example, if you decided at the outset to use a southwest decorating theme you would know which colors to choose for wall paint and to look for a southwestern style rug rather than a contemporary one.
But themes are very limiting and even if you just make a color scheme, you can get tired of it quite quickly (and you may find you whole house out of date before too long).
It may be best to have an eclectic mix of things you love while still sticking to design principles, such as balancing light and dark colors and using colors which work well together. It allows you to be both fashionable and flexible in your choices and you will end up with an interior which uniquely reflects your personality and not a style that you have just because you read about it on the pages of an interior design magazine. If this means mixing an antique chest of drawers with a hot pink rug then so be it.
Do your thinking over some time and allow yourself plenty of time for planning your decorating projects. These things cannot be rushed. You might like to paint your home in a neutral color such as cream while you get your ideas together if you cannot bear the thought of unpainted walls. That way you will not feel rushed into making decorating decisions you might regret.