Weald Walker, I will describe what I did.
Knowing that most people on the site are expecting to play some version of D&D or Pathfinder, I described my game as a fantasy RPG and I gave the setting. In my case the setting was late in the third age of Middle Earth. Since the setting was appealing to a lot of folks given the recent movies, I usually had some interest from players. I then met with them over coffee, beer or lunch and get into the weeds about the system and setting. I had pre-generated characters in my game and this has not been a problem.
I would not disclose in your message you are playing Rolemaster. Just your setting. I hope this helps.