that you are in a reasonably safe place to get out of your car if possible
Even if it is a small accident it helps to have a police report to go off of in order to figure out who is at fault during the accident.
Make sure the other person is okay. Accidents happen. Keep the situation calm and do not admit guilt or apologize. You never know what could be used against you later.
Make sure you get a valid insurance card. Look at the dates to make sure that the expiration date is a future date.
Take pictures of the intersection and road where the accident occurred. Take pictures of the other persons vehicle. Take pictures of your vehicle. Make sure you document as much as you can.
You can record these or have them write them down. Witnesses are the best right after the incident. The more you can gather the better proof you have that the truth will come out in the claims process.
He or she may not be able to give it to you right then but at least get the case # so you can call and request it later.
Get ready for all of the questions that the claims adjustor is going to ask you.
You can also file the claim later on if the other persons insurance is giving you the run around or a hard time when processing everything. Once you file a claim with your own insurance then everything is taken out of your hands. The two insurance companies work together to decide what needs to be paid by whom.
Accidents happen and the best thing to do is move forward and learn from your mistakes. Realize what you did wrong and try and not do it again.
Disclaimer: These are suggested steps to take based on my prior experience in dealing with them.