First I make sure everyone is alright. If not tend to them. If so, check the damage. Then either call 911(or the the cops directly) or have someone else do it. Exchange insurance info with the other person. Deal with the cops. Hopefully drive away if not wait for a tow truck and a ride.
Try not to bleed to death. Seriously, make sure that everyone is OK first then exchange info with the other driver involved. Get and give license number, name, address, insurance info. Get witness statements. Very important--get a police report.
Getting a police report is super important, even if the other party or even the police think that is not a big accident, demand to get a police report. Otherwise, you could be screwed. The police cannot deny you a police report in most cases.