Saw a great article a few days ago on the Softball Performance blog from Marc Dagenais. Normally Marc focuses on conditioning and strength types of issues, but in this one he offered some cool strategies for hitting the changeup. 

I have one to add, which is really aimed at getting hitters to wait back on slower pitching than they're used to. Telling them to "wait on it" is kind of vague. When hitters are used to seeing faster pitching (faster being a relative term), it's hard for them to know just how long to wait.  

What I will often do is draw a line in the dirt in front of home plate, and tell them not to start their swings until the ball crosses that line. Sometimes it's just 10 feet in front of home, other times it's further out. Sometimes I guess wrong and it has to move. But the principle still holds.