Usually I acquire books based on recommendations from book groups and friends who share my reading tastes. If it's an author I've enjoyed before, that's usually all the recommendation a book needs. Sometimes I'll get books from Amazon's recommendations based on what else I've rated and purchased. Sometimes a catchy title will do it...I have one book called "My Cousin, My Gastroenterologist" on the shelf that I picked up purely because I work in a gastroenterology clinic. Bizarre titles will attract my attention but it takes more than that to have me devour the book. I don't pay much attention to the book blurbs or synopsis on the back because those are often full of baloney--it's purely hype written by the publisher trying to sell the book and often bears little resemblance to the book inside.
What makes me pick up a book from the shelf just depends on which book happens to be making the loudest or most unique "read me!" noise at the time. I've got about 650 books on my TBR stacks at the moment so sometimes it gets rather noisy in here! LOL If it's a series book, I always choose those in order.
Whether or not I actually devour the book is wholly up to the author's skill at being able to suck me into the story, make me care about the characters, and whether or not the writing style flows smoothly.
I come from a visual arts background so I tend to notice the cover art first, unless I'm looking for a specific author's name. I have a group of favored authors and am always on the lookout for their books. Otherwise, I tend to follow the same five stages of book purchasing as most people:
1. Notice the cover/author name/title of book
2. Read the blurb and either put is back on the shelf if it doesn't catch my interest or continue to #3
3. Flip through the pages and read a few sentences from the middle
4. Open to the front of the book and read the first few pages
5. Buy the book or put it back
If I reach #5, I'm usually planning to buy the book. The only thing that would keep me from buying at that point is budget. However, I usually remember the title and author's name and will go back for it later.