Seek safety and medical attention first. Move to safety if you can, check for injuries, and call 911 if anyone is hurt. Even if you feel fine, some injuries don't show symptoms right away.
Document everything at the scene. Take photos of the vehicles, license plates, road conditions, and any visible injuries. Get the other driver's insurance and contact information, and get contact information from any witnesses.
File a police report, and be careful what you say to insurance adjusters — avoid admitting fault or giving a recorded statement before speaking with an attorney.
See a doctor promptly, and keep records of every appointment, bill, and missed day of work. This becomes the backbone of your claim.
Contact Alex before accepting any settlement offer. Insurers often offer a fast, low payout before you know the full extent of your injuries.