I was going to flippantly say "because an artist doesn't paint over a dirty canvas", but then I recalled that artists do indeed sometimes reuse old canvases, so that analogy is all shot to heck.

I'm not big into makeup, but washing first is just part of good hygiene, and gets rid of dirt, dead skin cells, and oils that might lead to skin breakouts and prevent your makeup from staying at it's best.

Going on the big date, to the prom, or modeling? Clean, moisturize, concealer or cover-up as needed, maybe a primer, foundation, powder, blush or bronzer (maybe two shades for highlighting and contouring). Eye shadow (two or three shades) eye liner, mascara. Lip pencil, lipstick, maybe a touch of gloss. Oh, and maybe a brow pencil, powder, or gel.

When repainting a surface (as in decorating rather than art), most people generally clean and sand it first, to remove dirt and grime as well as providing a base the new paint can grip. Without cleaning the wall first, you could be overpainting grease, so it might not stick or, if it did, look different from the rest.

I'd assume a similar approach applies to make-up: clean and scrub your face beforehand to remove dirt / grease / oils etc. as well as providing a consistent base for the make-up.

Skin has oil on it pretty much all the time. Some makeup reacts with this others do not choose carefully.

Washing one's face before makeup is a good practice but not entirely necessary, usually you have done this at least once since you woke up.

Moisturizer, again good practice but not necessary.

Concealer, its nice if you have flawless skin with no scars but that is rare.

Foundation, put on with fingertips rub all over face and upper neck. Use sponge applicator to smooth out all over.

Beard shadow, there is some products available to hide this however here is some tricks I found by doing makeup on crossdressers. Yellow eyeshadow will counteract the redness of razor burn. Leaving the top off of a liquid foundation bottle for a day thickens it making it more useful for coverage.

Loose powder, powder whole face.

Eyeliner outline the section or sections of your eyes. Outlining the whole eye is a waste unless you have really tiny eyes in proportion to your face.

Eyeshadow, this one is tricky but a good rule is if you have dust from the shadow falling below your eye your putting on too much at a time. A small makeup brush works wonders for blending in different shades for different looks. This is a trial and error practice. Powder below eye is best removed by cupping your hand infront of mouth and blowing. Using the still damp foundation sponge to blot overtop if you smudged it and put powder back on.

Eyelash curler, not the most fun device ever invented for use but it does make ones lashes curl upwards. start right at eyelid apply for 5 or 10 secs release a little move out on lashes to about middle squeeze again for 5 or 10 secs release a little move to end of lashes do again. Can be done with or without mascara on.

Mascara, apply over top of lashes and then underneath. Switch back and forth till each eye has about 3 coats then use a small eyelash brush to remove any blobs. For lower lashes its easiest to rub back and forth across lashes to bring them out. Use the tip of the mascara wand to do this. DO NOT pump the wand in and out of the tube. It doesn't help and in the long run drys out the mascara long before its time. Use a Cotton swab to remove any mistakes.

Blush, this is used seldom but there is tricks to this. For too high cheekbones apply a light shade on the underside of cheekbone. For low cheekbones apply a darker shade under the cheekbone. These are skin colors one tint off. On actual cheek put on a very light dusting of the color you want. Its best to use a large brush that is put into the blush color then tapped off. Run over cheekbone once on each side. The object of blush is to enhance subtly.

Eyebrows, its a good idea to brush them or add pencil to help make them uniform in appearance. Not touching these will leave you with a plain day look even with nightime eyeshadow.

Lip line, lip gloss, lip stick, These are entirely up to the person as to what you want to use. My advice is to only online a lip if it looks too small. Both lips should match. Some people have a big upper lip and small lower. Draw a line on the outside edge of the lower lip and fill in the color on the lips. Its best to use a lip pencil once shade darker than the lip color you will use. Lip color will vary on the person and face. A general stand by for most of us is a red of some sort that is close to our natural color. I myself use a moisturizing lipstick.

Depending on the activity you will be doing its not a bad idea to seal your makeup using a spritz of hairspray.

Not everyone can wear all brands of makeup. Nor is all brands either cheap or expensive. It's trail and error to find a good brand you prefer that does not cause a reaction. If one does experience a reaction wash your face with milk.

Skin care is a different section that is more of a personal preference than anything else.

Clean skin is happy skin. Foundation will clog pores, equaling pizza face (yuk). Wash up before bed (I moisturize then) and when you wake up, wash and a light moisturizer (the right oils can be your friend!)Then you start with a clean face in the morning and look like a fresh flower!!!

The other stuff is icing on the cake!

A good person to watch is Michelle Phan. She's my guru...

YAY!