Every hitter has their weaknesses. Perhaps it is a low, outside strike. Maybe they have difficulty with anything off speed, or pitches on the inner half of the plate.
In all reality, the strike zone, from the knees to the letters, ranging from the inner half to the outer half of the plate, is a fairly large area to cover with a 32-34 inch bat. Great hitters understand this, and they discipline themselves to lay off pitches they know they struggle with early in the count.
Successful hitters understand their strengths as well. They understand the pitch they hit the hardest and most consistently. Good hitting coaches ask their players to evaluate their best pitch to handle, as well as the pitch that gives them the most trouble.
Once hitters know the pitches that they like and dislike, they are well on their way towards developing a successful hitting plan they should have before entering the batter's box. This plan starts with an understanding of strengths and weaknesses. If the fastball at the knees is their best pitch, make sure they are looking for it early in the count.
More importantly, hitters should sit on the pitch when the count is 2 and 0 or 3 and 1 (referred to as hitter's counts, because in these situations the pitcher can ill afford to throw a ball). Countless high school hitters have become stars simply by banging out hits on 2 and 0 or 3 and 1 counts. These hitters know the pitcher has to throw a strike in this situation, and usually for a young, developing pitcher the fastball gives them the best chance to hit the zone.
Along the same lines, if the count is 2 and 0 or 3 and 1, the hitter should never swing at a pitch that is in a location he or she cannot hit hard. This is why it is important for all hitters to really understand their weaknesses. Remember, because of the strike zone's size, there are strikes that might not be good pitches to hit.
Good hitters lay off these pitches early in the count. Good hitters also understand the importance of working the count in their favor and taking an aggressive swing at their pitch. Hitters who are on the offensive always have a better chance of succeeding than those who are on the defensive.