As a hitter, effectively making contact with the ball is a critical skill to master. Many in the sporting world consider it among the most difficult techniques to fully develop. If it's so hard, why does every great hitter say you must never think when hitting a baseball?
It's because great hitters are made during practice. Hitting well involves the right body mechanics and focused training. If you weren't born with it you can develop it; if you train smart.
I believe hitting is the most over-taught skill in sports. It's quite obvious that a hitter needs a clear head when batting. This makes the practice of a hitting coach talking to a batter when he is trying to hit the ball seem even more absurd. I have no idea why they do this. This is the most effective technique for confusing and distracting a batter. Is this the goal?
Simplicity is the secret. Practice hard. When working on something, only work on one area of the swing at a time. When you've done enough work to engrain that into your muscle memory then you can move on to the next part of your swing that needs help.
Standing at the plate can bring on nervousness, but it's important to stay calm and relaxed. This zen-like attitude will allow your body to react instantly to the ball. If your muscles are tense your body will not be reacting at peak speed and quickness. Part of staying relaxed includes not grabbing the bat tightly when batting. Keeping a relaxed hold on the bat will help relax the body which will improve reaction time and hitting power.
Work on using your legs and trunk when you swing. One of the largest problems is only hitting from the waist up. The most famous sluggers use the body most effectively by moving from the core outward - engaging the hips, legs and having great form throughout. Avoid "squashing the bug". This is terrible advice and robs the hitter of virtually all of his power.
Last, but certainly not least, work on your baseball-specific vision. Learn how to track a projectile (i.e. baseball). Learn how to watch the ball as it travels through different planes and paths. Your vision ability when hitting is vital. Be sure to get regular vision checks. After all, you can't hit what you can't see!