You cannot cook an omelet without eggs (or egg whites for the health conscious folks). In the world of makeup, you cannot create looks without some sort of technique. Please take the time to learn your craft. Hone your skills by seeking out professional classes, workshops, or by talking to experts and practicing what you need to learn.
You need to have good techniques, like knowing how to blend products until they seem to “disappear” into the skin, and you need to know basic color theory. If you struggle with color theory, check out “Makeup Meets Color Theory” at Beautylish.com. Resources are everywhere, especially for aspiring MUA’s, and if you expect people to treat you like a professional, you have to learn from professionals. No technique means no pay, or very low pay.
Take pictures while you work, and use the flash, which shows all flaws. Don’t be afraid to stop and start over if need be, because a happy client is a repeat client. While no one should be expecting miracles, clients do expect their makeup artists to interpret their vision and make it a reality.
Try out new products that you’ve seen other artists use. If you need to save up to splurge on luxury brands from time to time, then you need to do that, so that you can have the experience of working with different brands. I’m no slave to any particular brand of makeup but there are some products that just work better than others. Always have your “go to” products as a part of your arsenal of goodies, so that you are always prepared to make up someone’s face at a moment’s notice. Invest in good tools, especially sponges and brushes.
You get what you put into this field of makeup artistry. If you invest in education, devote your time, put forth great effort, and practice repeatedly, this career can be exceptionally rewarding. Remember that no matter what you study and learn, you have to develop your own signature style and rely on yourself and your instincts to help you create work that you can be proud of for the rest of your life.