The first thing you always want to do is get medical attention. Also, make sure the police are called. It is important that there is a complete police report for several reasons. First, it is important that information is collected from all the parties and witnesses to the collision. Second, although the at-fault party may feel terrible and apologetic at the scene, people tend to want to change their mind once they fear repercussions from the insurance carrier; so it is nice to have them provide a statement to the police officer. If they later decide to change their story, it will appear less credible.
Make sure you seek medical treatment, even if you feel okay. Many times in motorcycle accidents, the adrenaline is pumping so hard that your body masks your true injury. Also, it is possible you have sustained a head injury without realizing it. So it is important to document that you were concerned enough about your injuries to seek medical attention.