Each case is different, and there's no one course of action that's true for every case. Generally, your lawyer will do some investigation and preparation before taking official action. She may even draft a demand letter or approach the other party's insurance company and attempt to negotiate. It's possible that your personal injury case could be resolved before formal paperwork is ever filed with the court.
The first official step in a personal injury lawsuit is filing formal paperwork with the court. Your attorney will file a document commonly referred to as the complaint. The complaint names the parties involved in the incident and lays out the facts. It also asks the court to take certain actions, like ordering that the other party compensate you for your injuries and other harms you experienced.
The complaint and a summons to appear in court will be served on the other party. Then, that party will have a limited amount of time to answer the complaint. The answer may concede certain facts. It may also deny wrongdoing.