First, I look for class and character options, to see if there's anything nifty there. Then I look at the bits of civilization and the over-all layout of the land. Then I look at the NPCs, and then check out some of the quest stuff. Then I look through the encounters. Then I will sit down and start actually reading it if anything looks particularly good, otherwise I just use it as a reference to steal ideas from and change to suit my needs.
I'm not a huge fan of pre-built adventures to be honest, they assume a level of linearity that I'm not a huge fan of. Even with OotA, you're only free to sandbox it up for a little while before something compels you to get back into the story. I like a well defined world that can stand on its own that also happens to have a storyline, with what happens if the characters ignore X event, so that I can feel free to plop them into the story at any point; maybe the party was off wandering a cave system that led to a sunken temple for the first few levels (days), and then they start traveling to a bigger city to sell off the loot at a better price and have access to better gear, so it ends up being a week or so before they even have a chance to find out about what's going on, then they ignore that quest line for a bit to go do whatever else, get somewhere, and the problem has spread further, so now they decide to come in and start dealing with it, and are having to go back and clean up the mess wrought by whatever story they were ignoring. I don't like to force anything on players, I like to give them a choice, and if they want to ignore the rise of demogorgon they are free to do so, but they suffer the consequences of their choice in the form of demogorgon disrupting trade, causing nations to divert resources, all of a sudden weapons and armor become harder to buy, potions are a no-go because of the war effort, etc. Still don't want to deal with it? Cool by me. Want to hop a boat and go to another continent? Sweet!
<.< I do really want to run CoS though, I just haven't had the time to read through all of it yet (have to learn a few new systems, so I can run them at a local shop), it looks fun and like, literally everyone who plays DnD is roughly familiar with it and thinks it's interesting, so players definitely wouldn't be a problem.