Hitting is more than smashing the ball; it's approaching an at-bat with an understanding of the game situation--and what a hitter's specific role should be.
Here are three areas any hitter can focus on to prepare successfully at the plate and become more valuable to their team.
Study the Pitcher
Anything you can pick up about the pitcher prior to going into the box can help give you an advantage. Ask yourself the following questions: Does she always throw the first pitch as a strike? What pitch does she like to throw when she's ahead in the count? Does she move the ball mostly in and out, or up and down? What's her "bread and butter" pitch? Does she have a tendency to throw inside or outside? Up in the zone or down in the zone? Does she tip off any of her pitches by how she delivers or prepares to deliver?
Some pitchers look at the location of where they'll throw their pitch after picking up the signal from the catcher. If you can pick up the movement of their eyes from the catcher's signal to their target, you may be able to tell where the pitch will be thrown.
Bring Confidence Into the Box
Go into your at-bat with confidence that you will hit the ball. Even if you're not sure you will, tell yourself you will. This should start before you get to the box. Do not let the pitcher see that you are worried or that you lack confidence. Going in the batter's box with anything less than a confidence demeanor is helping the pitcher. Note: Work on your body language in a mirror to ensure you're projecting confidence.
Most importantly you need to have the right mindset in the batter's box. Positive thoughts such as "I'm going to smash this ball" are far better than telling yourself things like "I hope I don't strike out." Great athletes know they're going to get the job done, rather than hope they don't mess up. Do the same.
Know the Situation
It's essential you know the game situation before getting into the box. What does your team need right at this moment? Does your team need to move runners into scoring position? Does your team need a hit? Or does your team just need to bring a runner home even if an out is recorded in the process?
Bringing a runner home from third base with two outs is very different from bringing them in with just one out. It's important that you know these types of things as a batter. With a runner on third and two outs, you basically need a hit to score that runner (or an error). With just one out however, there are many ways to score: passed ball, grounder to the right side, deep fly, base hit, etc.
Focusing on what needs to be done in a given moment will greatly diminish your level of stress and give you the confidence to succeed in all areas of hitting.