Be yourself, first and foremost. If you say something a certain way in real life, type it out that way online as well. If you act a certain way, translate that into your posts to give a sense of who you are.
IMO, during a first meeting online.. in fact for the first few e-mails .. there is no such thing as Dom/sub. There is me and a girl on the other end who I would like to get to know better. She is a person, not an object to use or to treat as some lower form or life. I am just another guy who happens to wander by. I could take this initial meeting two different ways: 1) puff my chest out and dazzle her with my Domly brilliance <gags> or 2) be myself while acting genuine and not putting on any airs about how I am the only Domly one around who has the power... yada yada yada.
True dominance will shine through your words, questions, and answers brighter than any contrived persona ever could.
Asking and answering questions and having a 'vanilla' conversation to get to know somebody is in no way submissive, it is human.