When choosing a foundation many people make the same mistake by buying one that is too dark for them or too pink or orange. This can make a person look a lot older than they actually are and whereas foundation is not supposed to be seen, choosing the wrong shade can make it stand out far too much and look quite awful.
Ideally you want to choose a foundation that matches your skin tone exactly, but this can be hard to do. Most people check foundation on the back of their hands, but the skin on your hands is often a different shade to that on your face. It is good to test a patch on your chin and neck to see if it blends in. If in doubt I would always recommend going to a shade lighter, as once you have added your blusher and bronzer you really cannot tell and this can often make you look more youthful.