Do you suit silver or gold jewellery better? If you suit silver, pick cool toned colours, if you suit gold, pick warm toned colours.
I think you can't do wrong picking out colours that feature in your natural colouring. So eye colour, hair colour, skin colour obviously. But also look at the colour of your lips.
Also, just hold colours up to your face in front of a mirror, and see what makes you look good. Avoid anything that makes you look washed out or faded,into the background.
I think it's also important that you like the colours you choose. Of the colours that suit me, I like deep greens, rich golden oranges, strong yellows and deep blush colours. I don't like browns. So I don't wear them. Then, that's where contrast comes in- black is too much, and whilst it would make sense for my natural dark base colours to be browns, I don't like them. So as well as forest greens I choose French navy as darks, even though generally speaking blue doesn't suit me. French navy has a slight yellowish tinge to it, so it goes with my warm colouring.
Coupled with cream rather than white, French navy shows the same level of contrast as exists between my hair/eyes and my skin. So because it works on the contrast level, I get away with picking a colour that isn't quite an ideal one for me. (Black and white looks too stark on me, Air Force blue and grey would be both too low contrast and also too cool,toned for me).