Philosophy:

House Thinking, A Room-by-Room Look at How We Live, by Winnifred Gallagher. Gallagher writes about the psychology and history of houses. Think about it: why do homes from the 1950s have closed-off, secreted kitchens, and most modern piles of bricks stop just short of putting a sofa in front of the stove? Don't know? Think about which you'd prefer, and why. A home says a lot more about how you live your life than you realize. Get it right, and you'll live at peace with your home.
Practice:

The House in Good Taste, by Elsie de Wolfe. This decorating classic was first released in 1914, and still sets a standard as one of the first decorating books published. While advice on your maid's quarters may not be relevant, most of the recommendations on layout and function for rooms are as relevant today as they were a century ago.
Inspiration:

Modern Glamor, the Art of Unexpected Style, by Kelly Wearstler. I'm a huge fan of Wearstler's - she's a tremendous talent with an unusual eye. And everything she does is big, big, BIG. While some of her work can be a bit intimidating, this book is wonderful for inspiration because a lot of the ideas in these pages are easily doable on a budget. The patterns, color combos, and plate and accessory groupings are superb, and just as relevant whether you bought your materials at Saks Home or the local flea market.
Happy reading!