I had face painted in the past, casually. Back in the mid nineties, I got a face painting book that came with the special face paints and used it to face paint my oldest son for Halloween each year. It was such fun, but I kind of forgot about it. Then, we had a new flea market coming to town and I was trying to think up what I could sell there and face painting popped into my head. I started researching. I bought the Palmer's face paint they sell at Walmart and since I'd painted before, I knew it wasn't the good stuff.
So, I found some quality face paint online to buy and started coming up with designs I could offer. They weren't the greatest, but at the time I thought they were good!

And so did my customers, so I think that's all that matters. I charged $2 for cheek art and $4 for full face. I didn't get a lot of takers at first, but I got the practice I needed and I continued to improve. I don't think you should wait too long before getting out there, even if you only work for tips at first. Painting a bunch of faces really improves your skill. You'll start to see what your problem areas are and work on improving them.