1. See a doctor if you hurt. If you delay you are hurting yourself literally and helping the at fault driver's insurance company later argue that you couldn't have been that badly injured or you would have promptly seen somebody.
2. See a lawyer pronto. Personal injury lawyers do not charge for initial consultations and even if you choose not to hire them, they can help you identify potential benefits and how to claim them. They can also tell you how to frame your description of the crash, so you don't fall into any legal traps.
3. Do not talk to the at fault driver's insurance company about anything other than damage to your vehicle. If they ask if you are hurt tell them that you do not wish to discuss that issue as you are speaking to an attorney about it.
4. Document everything. If there were witnesses to your crash get their names and get statements from them concerning their observations of who was at fault. Take pictures at the scene and of all cars involved. If you called your boss to tell them you were injured and can't work document this in writing by e-mail, text of good old fashioned paper.
5. Be honest with your doctor, your lawyer and your employer. If you hurt the same part of your body five years ago, it is better they know so their reports and legal presentations withstand later scrutiny.