@FrankHghTwr
Outside of Art Fight I prefer the classic way of asking first and chatting about what characters to even draw. Otherwise it's hard to tell from gift/fan art.

Personally I always follow the art trade etiquette: I see someone is open for trades, I ask them if they want to trade, we discuss what characters to draw, I give them my work first so they know I'm not someone who wants to scam them, then they (hopefully) make theirs and send it to me.