Do you judge a book by it's cover? Do you read the summary on it's back or inside cover? Do you skim it? Do you only read highly recommended books? How do you choose?

I go based on the summary.

Because I get most of my books as an ebook now there is no judge by cover. XD

I pick a book by its spine XD

Seriously, if the font looks interesting enough or the title I'll snatch it up and take a closer peek.

From there I first hit the back of it to read a little excerpt if there is one. If not I'll go for the innards and read the first few pages. If it catches me the slightest bit I'll go near the center and take in a bit... And finally... I'll decide whether or not its worth my time.

But if it is by an author I've already read and enjoyed the likelihood of my actually trying it out increases tremendously.

Several things:

The author, the title, the "theme" (no lovestories please) , the cover , the summary and most important: reading the first 2 or 3 pages if possible.

First the cover and/or titel must appeal to me.
Then I read the back.

And I often read what friends suggest.

I found out that i am more inclined to read a sci fi/ supernatural themed book than other.

So lately i am going for those that are regarded as good/best/popular and usually i am not disappointed (i am not an avid reader, i just read in subways or places where i want time to pass faster)

If i watch the movie, i might be really curious to know about the book it was based on (that's how i read Dune, Hunger Games, planning to read Ender's Game series XD)

I read the very last page first. If I like the end of the story, them I decide to read it and figure out how it got to be that way. Even if the last page only has a few sentances.

Fist is by cover, then I will read the summary and look at reviews and rating. Depending on what it is, if the summary makes it sound amazing, I will skip reading reviews, but if I'm still iffy about it, I will read reviews and make my decisions there. Sometimes the title gets me too (ie. A Thousand Names [I've yet to read it, but the title and cover looks awesome]) They just sound like they'll be the best and most interesting book I'll ever get a chance to read that I won't look into summaries and reviews and get the ebook to read. I;m also more tempted to buy books with pretty covers when I'm at a book store because some covers are really pretty ;~; I need to stop doing this, though, I have read some really stupid, boring, and/or just plain terrible books because of this.

I do ALL OF THE ABOVE.
Usually if I see a book cover that catches me eye, I'll read its synopsis, and if I like it, I'll read the first sentence. If I like that, I'll skim through it a bit, then buy it.
I won't read books that are extremely popular (like Divergent) unless it was recommended to me specifically by people I know IRL.

I made the mistake of judging books by their covers and recs by people I didn't know when I bought a few of the House of Night books (I don't have the second one because I bought them secondhand at a church book sale :P) and Blue Bloods books. I only got halfway through the first BB book and one chapter in HoN before I threw them both at the wall.
Now they sit on my bookshelf, yellowing and collecting dust. I probably won't read them all the way through. I might give them to my school library. XP