More Blue = Cool
More Yellow = Warm
Equal = Neutral
Another way to find out what skin tone you have is to compare your skin to the colors Silver and Gold. Generally if your skin looks good with Gold, you have a warm skin tone, Silver means cool, and if it looks good with both, then you have Neutral.
Sometimes it can be hard to tell on yourself, so you may want to ask a friend to help you decide.
Once you have decided your skin tone, it is time to choose a Concealer, Foundation and Powder. Depending on where you buy your cosmetics from, you may have a hard time figuring out which one looks best on your skin tone.
After this, the best way to choose a Concealer, foundation and powder is to try it out! Generally for concealer, you should pick one that is a shade lighter than your natural skin tone, so that when you use it to cover dark areas and imperfections it will blend and look natural. If you have a lot of red spots (acne, scars, etc.) then you should also look into getting a Green spot neutralizer, you use this under concealer to neutralize the red spot and make it look natural. After you have chosen the right concealer for yourself, you should choose a foundation that matches your skin tone as closely as possible. If you have freckles it is recommended to match the color with your lightest freckles to help even out your skin color.
Then, it is time to choose and apply a lip color. I recommend lip color before your other cosmetics because if you apply lip color after everything else, you are likely to put it on darker, to "match" the intensity of the other makeup you are wearing; by applying lip color first, you will achieve a much more natural color with a subtle look.
Generally you should match your lipstick to your eyeshadow, keep it in the same general color family, so if you are wearing pink eyeshadow, try a similar color lipstick, maybe a shade darker or lighter. Grey eyeshadow looks great with different shades of red lipstick! As a rule of thumb, if your eyeshadow is shimmery, you should avoid shimmery lipsticks, and vice-versa. I recommend to all of my clients to DAB lipstick and gloss on, not to swipe it across their lips. By dabbing you have more control over the intensity of the color and you can make a more natural or bold look.
After this you should choose an eye shadow. Again, depending on where you purchase your cosmetics you may have trouble finding shades that look good on you as they aren't always labeled for skin tones. From my experience I have found that for Cool skin tones, Pinks, Berries and Blue/grays seem to look best, for Warm skin tones Earth tones tend to look best (greens & browns and some reds ESPECIALLY for redheads), and for Neutral Skin tones, I try to combine the 2.
After you have chosen and applied the appropriate eyeshadow, you should apply an eyeliner and Mascara. For people with light colored hair, brown or brown/black is an excellent choice of eyeliner and mascara. For people with Darker hair, Black is best, Although black looks very dramatic on anyone, it is a great choice for evening time.
As with everything, this is just a guideline, play around with your makeup, take whatever seems helpful and leave the rest, this is just meant to give some suggestions, the best way to find out what looks best on you, is to try different things out! Good luck!