I consider book stores as my comfort zone in the same way a fisherman finds solace at sea. May be this is why I call my book-finding adventures as trawling for books. Like a fisherman, I cast my net far and wide hoping to get a bounty of a catch in book choices. I set aside those whose titles and/or authors may interest me or my friends and put back in the shelves/bins those that don't.
Books are neutral gifts for friends because they don't have a loaded meaning like giving a deodorant spray or sexy underwear. I try to remember or surmise what type of books might interest a friend (Is s/he passionate about it, is it job/project-related, is it something s/he can learn anything from?).
If it were just for the sake of gift-giving (like for a Christmas party where you don't really know who'll get the exchange gift you brought), any book will do. But I take time to discern how my friends will be delighted/enlightened in reading their gift-books. This friend misses his father so much, I think this book on fathers and sons will soothe his feelings. That doctor-friend may be surprised to know that medicine is not only good for textbooks, but also for short stories and essays. This book on practical foreign language phrases might help this friend communicate better with her fiance.
It doesn't need an occasion for me to give gift-books. When the right book comes out of my trawling expeditions, I feel giddy to buy it for the intended reader. So, my friends should not be surprised when I approach them, smiling with a book in hand. Each gift-book comes with this: I immediately thought of you when I saw this book. I'm happy to be the bridge so this book can cross over to you.