How to work on accuracy?

You don't give much to go by.
Nibbling is bad business in my book and relects lack of confidence in ones stuff and or mechs. As a 2012 guy have you stepped say from a freshman squad to JV or varsity? That can do it too. As the zone shrinks as you go higher..level by level.

When your concentration breaks the time tested thing is to step off and readjust (Rub the ball up, tie your cleats, clean spikes, rosen bag...etc). Some guys write key words or phrases in their cap bill to remind them of stuff.

My suggestion is to get yourself satisfied with some good mechs, solid conditioning and go out there with confidence..you gotta believe in your stuff and know you'll win the battle. It means attacking the batter.

WaphtuoS,
I agree with JD that it isn't alot to go on but I think one factor may be that you are growing. I know from working with HS level kids in the past that you had some pretty big growth jumps from year to year and figuring out how to time up that new frame can be difficult. Have confidence in your stuff and attack the hitter. If you nibble you will get in trouble. Get ahead and then expand the zone. Strike one is the best pitch in baseball and learn to be able to get ahead with the FB and a secondary pitch to keep hitters off balance. Once you get ahead you can dictate the at bat.

If you are consistently wild meaning that you are usually high, low, etc than it may be mechanical. If you are generally more wild all over then that is a little tougher to pinpoint.

Good luck

Good advice so far. One thing is to work with a good pitching instructor. Another thing is simply repetition. You need to throw as many bullpens/flatgrounds working on repeating your release point as your schedule/arm health will allow. My recommendation is to work on two things with your fastball. One is to find a location in the strike zone where you can throw a strike almost every time. Devote part of a pen to trying to throw as many strikes as possible throwing to that location. For example, throw ten pitches to that target and see how many strikes you can throw. As you get better at it stop giving yourself the marginal pitches. Ideally you should eventually be able to average 8 or 9 strikes out of 10 pitches. This is a good drill to do with one of those pitching targets because either you throw a strike or it bounces off it. The idea behind this is to have a pitch you can go to when you are behind in the count. The other part should be working on hitting locations with your fastball. I like working a few pitches a foot inside, a few a foot outside, a few on the inside corner and a few on the outside corner. Other times you may want to pick a certain location, i.e. low and outside, and focus most or all of a bullpen on hitting that particular location.

As far as practice, what I always tell pitchers is that every time they pick up the ball, it should be considered target practice.

Pitchers only get some many throws a day, so they have to maximize every one of them.

Stu

All major league pitchers can throw strikes but when they struggle with control it is a mindset issue. I would recommend Tom Hansons book heads up baseball for the mental approach. You can find his book on Amazon. He is also an advisory board member with The Pitching Academy.
I would also recommend adjusting your mechanics ensuring all of your momentum is going toward the plate. You can see great mechanics videos on you tube like this one.
http://www.youtube.com/watch?v=6VWnineQtTg