My first Pokemon Game was a used copy of Pokemon Black. It was a gift, given in a little plastic bag, no case or anything. I was SO excited, I opened it up on my Blue DSi and saw that there was already a save file. In my ignorance, I simply clicked "New Game'. Some time later I tried to save for the first time, and found I couldn't, because there was already a save file. I was inconsolable, it felt like such a huge deal to little me.
I was able to start a new save properly the next time with the help of my parents. All I remember from this now is that I named my starter Tepig TEPIGGY in all caps, and filled my party with Patrat and Lilipup.