I know this is a HS question, but I wanted to share my view on the differences on HS/College vs. pro ball regarding the curve ball. HS/College games aren't scouted/charted as heavily as pro ball. Usually, the best scouting report you'll have in HS is what you see that day or what the pitcher did last year. Pro hitters have much more info/data to work with, so "looking for a pitch" is really an educated guess and not a flat out guess.
Pitch recognition is critical with all pitches. If you can't see it, you can't hit it. Spin is usually the best indicator for the CB, but some will also come out of the hand higher than a fastball, as others have already mentioned. The better pitchers will have consistent deliveries and hide their pitches well.
After pitch recognition, the curve ball presents two specific issues a hitter must deal with - timing and movement.
Curve balls are slower than fastballs, so you'll have to practice hitting balls coming in at various speeds. Set up an L-screen 15-20 ft from home plate and have the ball flipped the ball underhand inside/outside at various speeds. Take a lot of swings (think thousands, not hundreds) specifically letting the ball travel/get deep and staying inside the ball. Don't allow yourself to roll over more than a couple times in a row - change your mental approach if you do.
The movement aspect of a curve ball can make it difficult to know if the pitch will be a ball or strike. A curve will often start as a ball and finish as a strike, or start as a strike and finish as a ball. You need reps to develop the discipline swings at strikes and taking balls. A two-wheel pitching machine can simulate a curveball if you don't have somebody to throw them to you consistently.
You often hear coaches saying, "Hit it the other way," but you still have to hit the ball where it is pitched. The verbal cue to hit it the other way speaks more to the timing aspect (letting the ball get deep, staying inside the ball) than it does to the movement. If its inside, stay inside the ball and pull it. If its outside, stay inside the ball and drive it the other way. If you've worked hard to establish your timing, you can just focus on seeing the ball and hitting it where its pitched, just as you would any other pitch.
One last thing... you can't bail out! If a curveball is thrown at you (righty vs righty, lefty vs lefty), it should break back toward the plate. When I was a sophomore in HS, a senior told me to "stick my front shoulder on it" which helped at the time. If you see a pitch coming at your head and you think its a fastball, why wouldn't you move?! This just takes some getting used to and is a pitch recognition issue, and even a great curve ball can freeze you up. You'll see MLB hitters lock up on Baseball Tonight's "That's Nasty" segment all summer long.
And a video for fun - walk-off home run I caught on video this summer. Hanging 1-2 slider that stayed up and over the middle. Whoops. For the timing aspect, watch when and how (soft/quiet) he gets his front foot down. (Maybe he should have hit that the other way?)
http://www.youtube.com/watch?v=J0r1vRM0kts
"Baseball is like church. Many attend, few understand." - Leo Durocher