[Teresa Edgerton]

I don't know who it was that told you not to use 12 point, because it's been the industry standard for decades. You'll find the occasional editor who doesn't mind 10 point -- and even more rarely (usually for electronic submissions) one who prefers it -- but in the vast majority of cases 12 point is what they want, so it's by far the safest way to go where an agent or an editor hasn't expressed a preference.