when you go to buy it make sure that you aren't already wearing any make up. clean washed skin is the best canvas.
You also need to understand that the same foundation isn't going to last you through the whole year as your skin will darken in the sun and become more pale in the winter. go in a speak to a consultant as they will be able to highlight zones that you need to concentrate on eg if you have dry skin you will need one with added moisturiser etc. Just keep your wits about you because they will try and sell you the entire collection!
Don't test it out on your hand because it may be a different tone than your skin on your face. Also, a professional at any department store should be able to help you pick out the shade for you, but never simply guess without trying the foundation out first.
Find the two shades that come closet, buy them both and mix them at home everyday. You'll be to readjust the pigment level to match your natural colour which can change from day to day anyway.
Don’t just get a product because it works for your friend. When you’re in a shop and buying a product, ask for a tester, never buy anything immediately. For foundation – try it on and look at yourself in natural light.
go to a department store and get your skin matched by a professional they will not only advise you about colour but also about what formula is best for you ie: what sort of finish you want, then ask to take away a sample of the chosen colour and try it, before you buy!
I find Laura Mercier to have the best foundation colors. They have an online store that shows the colors, but it's really best to find a company representitive of theirs and have them apply it your first time. I've always been rather pale, and clinique tended to give me an orange-ish look.
Make sure you get outside into the daylight. If it looks good in the daylight- it will look good in any light.
I recommend trying Prescriptives foundation- it's really good, and you can have it custom-blended to suit your skin tone and type.