Coach West and I up here in Northern Morrow county agree with ifubuildit. Those are 2 very informative sites.
Personally, I feel that you should be taking lots and lots of swings from a tee, making sure that you are moving the tee into different zones. That is, working inside and out as well as high and low. Very few pitchers throw right down the middle of the plate, but that is where a majority of girls want to work on their swings.
There is much debate as to a softball swing VS a baseball swing. Your best bet is to make yourself as knowledgeable as you can about hitting and find a reputable hitting coach, even just a few lessons could help your swing.