After contacting the police, you should contact your insurance company. The most important thing is honesty. Defrauding or attempting to defraud an automotive insurance company is a felony in many states. Even if the fault is not determinable, you should still contact your automotive insurance company. In the case of an underinsured/uninsured driver, your insurance will assist you.
First, make sure you know your policy. If you feel entitled to certain benefits, like no-fault coverage, then make sure to make that known to your insurance company. Your insurance company will take down all your information. They will ask you for the specific details of the incident. Be sure to be honest and tell them as much as you can. The more information you can give, the better. It will help the insurance company figure out the claim quicker. It may be a good idea to get the name of the representative you talked to. Write down everything they say and repeat it back to them to verify that you have everything right.
It is important to note, DO NOT SPEAK with the Insurance company of the other driver. They will record your conversation and try to use it against you. Speak with an accident attorney first so that you have someone in your corner fighting for your rights.