Right after the wreck
First of all, don't make any statements to the negligent driver's insurance company. Sometimes, they will call and try and fool you with loaded questions and exclude your claim on a manufactured liability defense. Second, if you are in pain, go to the doctor. Most of us men will not go to the doctor unless our leg is about to fall off. We do not take medicines, and we don't like hospitals. However, the insurance company will use this against you. They will argue that since you did not go to the ER or to your doctor the next day, you were not hurt. If you are having problems, then get checked out.
Dealing with the insurance company
First, watch what you sign. Sometimes, insurance companies will send out "hit squads" to get people to release their claims in exchange for a verbal promise to pay the medical bills. Don't do that. If you sign away your claim, they will sometimes deny any verbal promises. Also, you may have lost wages and future medical expenses that they will not cover. Second, prepare your case. You will need to obtain copies of your medical records, any lost wage information, copies of photos of your vehicle and the scene. The insurance company requires an incredible amount of information before they will process your claim. Make sure that you don't over-state your claim. If you are only having pain at night after work, then don't try and say that you are in constant pain. Not only is that wrong, the insurance company will typically check up on you.