A huge pet peeve of mine is dirty make-up brushes, so I like to give mine a good cleaning once a month or so. Instead of buying expensive cleaning solution, I go for the cheap, easy version: the Dove beauty bar! The beauty bar is SO inexpensive and it leaves my brushes so clean & beautiful.
The process is super easy. Take out your make-up brushes, your eyelash curler (& your tweezers, too!) and lay them out on a towel. Just wet the beauty bar under your sink and start brushing your brushes up against the bar. You'll start seeing ALL of your make-up go down the drain, which is such an awesome sight. Then, keep brushing them against the bar of soap until you don't see any make-up in the sink anymore.
Simply lay them flat on the same towel after rinsing, and by the next morning, your brushes should be good as new! It only takes about 10-15 minutes, and it's so worth it. Kind of soothing, too.