The Complete Book of Garden Design, Construction and Planting - David     Stevens, Lucy Huntington, Richard Key
De-mystify the whole garden design project.

It starts with basics, but doesn't condescend. As someone looking to learn about English gardening I appreciated the advice on aspect (South Westerly is best) and drainage.

A comprehensive beginners guide.

But if you're actually planting, I'd find a good local nursery and include its people's local knowledge in your plant choices. Also, the old advice of walking around your neighbourhood and seeing what grows well was skipped in this book.