There are many different brands of professional face paint. I sell Diamond FX and Snazaroo brands which I use. Also glitter, Snazaroo brushes and sponges. The sponges come in a round size and then I cut them in half to get the edge to work with.
When I first started out, I bought cheapo brushes from Walmart and really I found out that you can paint better with better brushes. So now, I use artists brushes from craft stores and my Snazaroo brushes. My favorite were the Royal Majestic, but I don't see them anymore at my local store.
The glitter needs to be cosmetic and not craft glitter. I like to add glitter after I've sponged on a base, while the face paint is still damp... it sticks bettter that way. Then I add the linework.
There are many good books and videos on face painting. Youtube is great to see many great face painters in action.
I would start out with a list of maybe 5 good boy faces you'd like to offer and 5 good girl faces, start browsing designs until you find elements you like and then start practicing. That's how I started out. I came up with a certain number of boy and girl designs full faces and then cheek art and then started practicing. Take lots of pictures and you'll have a record of your improvement, plus great pics for your board. A great way to improve is being out in the field. Maybe do one free event to get your feet wet. I'd recommend picking a really busy event. These are all things I did when I first started out, so everyone may have different experiences and preferences.
I did our local towns Julyfest when I first started out and I didn't charge. I was busy from beginning to end and it was such a whirlwind, but I learned a lot and noticed that I did improve. After this event I started charging, but it did get my feet wet.

When you keep getting the same face again and again, you can learn. You notice what you did wrong with the first face and then immediately, here's a new person wanting the same face, so you have your opportunity to tweak it and try something different.
Are you artistic already? If not, I would recommend the book, "Drawing on the Right Side of the Brain". That book really helped me to look at things differently... to look at how they really appear, to be able to draw them more accurately.
Hope this helps.