John,
It's always good to experiment with different pitches and I would never discourage that. The idea is to master your fastball (the more movement the better), have a change of speed on the fastball, and have a breaking pitch. Let me tell you what you need to compete as a pitcher in roughly the order of importance.

1. The ability to throw a strike with your fastball
2. The ability to throw a low strike with your fastball
3. The ability to throw a second pitch for a low strike - in order of importance change up, breaking ball (slider or curve), any other pitch
4. The ability to throw a second pitch for an out - it looks like a strike and gets a swing and miss
5. The ability to throw your fastball to different sides of the plate and to elevate the fastball.
6. The ability to throw a third pitch for a strike whichever pitch works best

Take a look at this list and understand these things - this list is in order of importance to a pitcher so spend your practice time accordingly, you will have days when you can do all of these, days when you can do some of these, and days when you can do none of these - figure out how to win on all of them.

When you look at this list realize that to fully have the ability means roughly 8 of 10 times you succeed. If you can throw a strike with your fastball 8 out of 10, practice throwing 8 out of 10 low strikes with your fastball. If you can do that, practice throwing your second pitch 8 out of 10 times for a low strike and so on.

By the numbers: 1 pitch to 1 location (down) you'll get by, 2 pitches to one location (down) you will be good, 2 pitches to two locations (down & inside outside) and you'll be excellent, 3 pitches to two locations and you'll be outstanding.

Go for it!

Pat

John,
Sometimes pitchers will see their stuff so much that they can't tell that it's moving. It's always a good idea to ask your catcher what he thinks.

Meanwhile, I answered another question about throwing a curve ball. It might help you with your slider or other breaking pitch.

http://www.weplay.com/questions/1689-can-i-have-some-tips-for-throwing-a-curve-ball#answer_8149

Pat

I don't know how old you are John, so I will speak in generalities. Until your senior year in high school work on placement with your fast ball and change up. The strain on your arm throwing most other types of pitches is too great at a young age. Mastery of these to pitches will improve your later use of other pitches. Any clinic I have ever attended always stressed the importance of these two pitches and that college scouts are looking for this.

thanks i can really control my fastball. and my slider is becoming real nasty.
i pitched in a pick up game the other day and they just couldnt hit me when the
usually were nailing the ball. mostly on the ground cause i work on that alot, but
this time was amazing and my friend who catches for me says my fastball gained some speed and my slider seems to start outside the right batters box then is in his glove right in the middle of the plate. thanks. im gonna keep practicing. but i have a really hard time with my change up.. dont know why but now it feels all wrong but thanks.

A strike