Which is always the first step in dealing with an accident in the lab?

Answer: inform your teacher of what has happened!

This depends on the type of accident that occured. There are major and minor accidents. On both types, the procedure is to keep calm and safe. In a minor accident, once in safe place the next thing to do is to notify the accident to qualified personal, it could be a supervisor. In a major one it's necessary to call the local emergency responders or a safety department, they are trained for this situations and will know what to do.

Be aware that each laboratory has a Laboratory Accident Response and Reporting Procedure. This is elaborated depending on the type of laboratory and material used in it.