Go to silverlining.org for some good info on kids with bipolar.ANd if you don't have a copy of the book, The Bipolar Child - GET IT. Even if you have to check it out of the library. It's fantastic and will help you get a handle on things and where to start.
Second thing we did was keep a journal & mood chart. It really helped us see the moods fluctuate dailey, and worsening weekly. Also, we saw what certain meds did to him. It was a bit harder for his DX because he has ADHD also. We had to look at other behaviors to see wich disorder was causing problems. Like if he was very hyper, we had to look at sleep patterns too to see if it was the BP causing mania.
Here are some great article on BP vs ADHD. Add the W's