Common mistake -- you might want to look into Patrick McKenzie's material about consulting. Some clients you'll even be able to say "I'm raising rates" and just start getting more money for the same work without issue.
I doubt it's going to be that easy, because some clients already balk at the current rates. It greatly depends on your niche, that's why I asked the GP what he was consulting on.
Clients always balk at rates. Fire the worst ones and keep the ones who pay up if you can. You should always be looking for better clients (i.e., doing outbound sales) if you want to charge more.