What is the first thing you should do after being notified your being sued for wrongful death?

Not knowing where you are, I cannot answer with certainty; however, depending upon the allegations in the complaint, if you had insurance that might cover the occurence/claim, report the complaint/lawsuit to your insurer and request that they defend it.  If you had no insurance applicable to the occurence/claim, my recommendation would be to seek an attorney to defend you assuming you can afford it.  If you cannot afford an attorney, you will still need to file an answer to the complaint within the time stated on the summons.