One more note-- if you're including ruffles across straight seams, like the pants legs, it works just fine to cut strips straight across the fabric. However, if you want to go around curves, like on a collar or scalloped hem, you'll need to cut the fabric on the bias, and follow the steps for making the ruffles. Bias-cut fabric curves around edges without sticking out at funny angles, if you've never used it before. I use a lot of hand-made bias to finish things-- a little time consuming to make, but so useful and pretty!
And here's a little before and after that's been in my "in progress" pile for a long, long time.