1. Skip the eyeliner and use dark eyelash glue on the band of the false eyelashes! Sometimes, I don't bother with applying the gel liner or pencil liner when I know I'll be applying false eyelashes to someone. The dark eyelash glue that I use (Duo Dark Tone) doubles up as a dark black eyeliner when applied. As a time saving bonus - I don't have to put mascara on the top of the person's lashes since the false lashes are usually overpowering anyway (also lessens the risk of eyeliner/mascara smudging/running throughout the day).
3. Powder brush! A powder brush is a must have in everyone's makeup kit. If I am in a hurry, I use the powder brush as a multi-purpose brush. After finishing a persons eyemakeup, I use it to sweep away any shadows that fell onto the cheek. After applying foundation and concealer, I use it to roll on some powder and brush off excess powder. I also use it really quickly to apply powder blush on the cheeks and bronzer powder on the temples, hollows of the cheeks, and jawline. It is faster than reaching for a disposable sponge, blush brush, and bronzer brush.
4. Carry disposables! If you're a makeup artist, you probably already carry disposable mascara wands for your clients. It is equally important to carry disposable lip brushes, disposable eyeliner brushes...etc! I have had to use disposables when I had no time in between to clean my brushes for the next appointment (e.g. doing a 5 person wedding in the morning, and rushing to another 5 person wedding after that!). Sometimes I wish I carried a little midget with me so he could clean my brushes in the car while we drive to the next appointment. Disposables will save you time (especially when you have no time) and they're clean and sanitary to use on your client. This has saved my butt a few times now.
5. All-in-one primer, foundation, concealer, and powder! This is one of my secret weapons introduced to me by one of my teachers a couple of years ago...The Motives Liquid Mineral Foundations. It's a primer, foundation, concealer, and powder in one. I go through tubes of the Linen (for caucasions like MAC NC15), Cream Beige (for Asians around MAC NC20), and Almond foundation colors (for tanned people or Indian skin around NC40). It has a primer in the foundation already and dries so that you don't need to set it with powder. It is creamy and thick enough to keep building and cover under eye circles and blemishes. Although it is a product that is marketed like Avon, Mary Kay, and Amway...the foundation is actually really good and saves me time digging for my primers, concealers, and powders! If you're based in Edmonton, you can pick some up from SunDaze Tanning (which may run you about $25-$30 for a tube but is well worth it!).
Hope some of these tips and products were somewhat useful in helping save time on makeup applications!