Characters, story, setting, and originality draw me to a book. Sometimes it's the author if I've read and enjoyed the author's work before, sometimes it's good reviews (but only if I know the reviewer). Mostly it's characters and plot, because without those the story tends to not be too enjoyable. Originality is something I like, but it's hard to find a truly original story these days so it takes a backseat (though I really like seeing new twists on old concepts). Setting is a nice bonus, especially if it's immersing and well-written in with a nice knowledge of the setting (so there are no weird holes in the map or names of regions that don't match the names of characters).
If a story looks like it has an interesting premise, a neat visual aesthetic and fun characters, that can get me to pick it up.... but mostly I stick with word of mouth, or creators/authors that I already know I like. When I'm browsing a library or bookstore I always end up picking things from authors I know first, then things my friends/family/the internets have recommended to me, then things that look like they could be fun but which I've never heard much about one way or the other.
It's hard to say, but generally, if the story looks interesting and have well-defined characters, I'd pick it up. I also like originality...I get tired seeing variations on the Tolkien or D&D world so I like to see something different other than the usual elves, dwarves, etc.
I usually get drawn in by recommendation of an Author, so I guess my juice is the creator. If a writer has a reputation for skill and craftmanship with their characters then i'm in. IF you want recommendations for that then George R.R. Martin and Dan Simmons great recommendations! lol
The reviews (including the blurb on the back of the book/DVD/game) are what attract me, but the story, character development, and imagery/visuals (in that order) are what keeps me engaged. Character development goes double if it's an RPG where you develop your own character: I love to role-play.