So for the most part people's ATRL usernames aren't their first names. Basically just state your name (or your preferred name).
I'll go first:
My actual first name is Diamond, but for most of my life I've just always gone by my middle name, Tia. I meet another "Diamond" every now and then, so it's better being referred to by my middle name.
My name is Taryn. I like that it's uncommon but people have such a hard time pronouncing it. They'll call me Tara, Kara, Karen, Terry, etc. It's not that difficult to say, it rhymes perfectly with the name Erin. But people still can't get it right. I still love it though because I'm normally the only Taryn around