The BIGS [PSP]
You can get a very easy homerun at the Metrodome (where the Twins play). Have all of your hitters aim towards right field. The balls will barely clear the fence, but because it is so big they cannot rob it. The same strategy works at Fenway Park.
To get doubles consistently, get your timing good enough so that when you hit the ball it says "Perfect". Then, aim your towards the opposite field and hit the ball. If done correctly the ball should one hop the wall. The only players that should not make it are the ones with one star for their speed. If you have someone fast (for example, Grady Sizemore), you can get a triple.
Have your power hitters first and your weak batters last. When you use your power hitters, try to smash the ball. With your weak hitters, they are usually fast so do not try to kill it.