Start with books and magazines. Start collecting images of things that you really love and see if you can find a common thread; do you lean modern, traditional, transitional?, Do you love muted colors, bright color., high contrast, low contrast? minimilistic or highly accessorized ?. Then see if you can't nail down a concept (which is much like theme but not so literal). For example right now I'm doing our Master bedroom and my concept is the marriage of masculine and feminine. Then come up with a color idea. Use paint chips to represent the colors you want to introduce. Not that you will apply them all as paint, I used an orange paint chip to represent my accessories. I just wanted to have the color idea in a physical form so I can look at it and analize it. With your concept established, start collecting images of actual items, paint, furniture, fabric, art, accessories, lighting. Don't commit, don't purchse anything!!!!!!!!! Put all these things in a binder, or on a collage board and dream, think, reasearch, budget. You may find somthing that you fall so in love with that it make you want to change your whole concept, and by all means, you should. Keep it loose in the begining. Develop multiple concepts and clolor ideas if you want before you hone in on one. The worst thing you can do is go and invest a lot of money is something before you've determined the whole space. Because then you are commited and you may find you wish you had gone another direction. I am a degreed interior designer and the saddest thing I encountered was when people went out and bought furniture with out really thinking it through. Often commiting to colors, and styles they didn't end up loving or even worse, a collection of furniture that looked great in the showroom, but didn't fit at all in thier space. Furniture stores have terrible return policies. The main thing is, find your style, commit to a concept, shop (but don't purchse). Get tear sheets for furniture, take pictures, photocopy books, and print from the computer, gather swatchs and paint chips. Put it all together tweak here, tweak there, budget the items you want, and when you are certain you love what you have collected, then execute: purchase, paint, intall. Very few people can design as they go and end up with something fabulous or without regrets. Most people who design as they go end up with somthing we like to call "hodge podge". When I did restaurant design, we had the art selected and placed on the walls in our documentation before foundations were poured. After all, how do you know where to put the lighting if you don't know where the art is going? My point is, think through as many details as possible before you commit or you will find yourself wishing you'd done this or that.