I used to work in a theatre as a makeup artist, and I specialized in corrective (Glamor is the street term) makeup, and later I began working in haunted houses and special effects.
Being able to do your own makeup is not the same as doing somebody else’s. YOU know what you want, so you’re able to replicate it. On somebody else, you have to take their best description (Which is not always what they mean or accurate) and then hope for the best. I frequented makeup conventions in Anaheim and it isn’t like you can walk into a salon and say, “Hi, I’m so and so and I’m going to do makeup.”
Practice, and make what’s called a “Makeup Bible.” Every time you do you, or somebody else’s makeup, document it. Anyone who wants to hire a makeup artist will flat out ask you for a makeup bible. Just going, “Uhh.. I have what’s on my face?” is not appropriate.
Take pictures from three sides.
Document what you used, the brands, colors, shades, brushes used, powders, toners, everything. Be as detailed as you possibly can. Some companies and salons may not care about your products used, but it makes it look good on you that you know the exact shade, style, color and brand of everything you’ve used and you can identify it.
Study up skin allergies and how to combat them. You may be fine with Witch Hazel, but someone else may not be. When I was running the makeup room of a haunted house, I had every actor show up the day before and I did a skin allergy test. Surely you can’t do this with clients, but you need to know the symptoms and alternatives to skin allergies. Anyone can have a reaction to anything, even those hypoallergenic mineral makeups everyone and their brother advertises. Know solutions and workarounds. Can’t use witch hazel? Try a tea tree oil toner instead. That kind of stuff.
Make sure you have a religious clean up program. Maintain your brushes, sponges and makeup case. You can get away with using your own brushes multiple times before washing, but in a professional environment, this is the biggest nono known to man. I used mostly cream makeups on-stage, and to ensure sterility of every actor, I used a CD disk. I would apply the amount of makeup I needed with a cleaned off makeup spatula, and each actor would have their own CD. At the end of the day, I could throw the CDs away, or sterilize them in hot soapy water at the end of a show. You need to be absolutely 100% here — you need to get a pattern down that everything is cleaned immaculately after every client.
Be knowledgeable about different styles, makeup brands and carry samples of each. If somebody walks in and goes, “I saw <designer here> had a really awesome eye shadow…” unless it’s an indie company, try to be able to recognize it.
Be well versed in as many styles as possible. You may like smokey eyes, but someone else may not be. If someone gives you a general term like, “I want it to be dark in the middle and feathered out”, you need to be able to plot this out in your head and make it happen. Makeup is forgiving — you can always wash it off and try again, but clients are not patient people, and if you were doing it for a theatre, or for a wedding, or a fashion show, directors and coordinators are not patient people. You need to be able to do something right the first time.
It sounds kind of harsh the way I worded it, but doing makeup is one of the best things I’ve ever done. I’ve met a lot of fantastic people and I’ve learned so, so, so much. Knowledge is power — devour as much knowledge you can get your hands on. Take a college course in makeup, even stage makeup. You learn a lot of tricks of the trade that you can apply to real life, and, good luck!