First make sure that you take great care of your face. Applying makeup is much easier if you have a nice canvas to start with. It's importnant to be knowledgeable about your skin type--oily, dry, combination, normal--because the amount of oil your skin produces will affect your makeup application and the kinds of products you'll buy. For example, girls with oily skin will benefit most from mattifying forumlas and powders.
Generally it's best to spend more on foundations and powders; and less on mascara because of the shelf life (mascara is good for about 3 months while foundation lasts a year) and also because foundations and powder have direct, long term contact with your skin. (Don't want your lively face to absorb nasty chemicals, right?) Speaking of price, sometimes expensive isn't always the best. In my experience I tried some MAC foundation only to discover it made my skin break out. What works for some people might not work for others.
As for application, for foundatioin alone, there are about 5 ways depending on its formula (liquid, poweder, aerosol, cream, mouse). Simply experiment to find out which method works best for you.
Finally, cleanliness is really importnant. Make sure your tools (fingers or brushes or sponges) and your face are always clean (freshly washed) before applying makeup. And at the end of the day, always remove your makeup. Simply use a makeup remover followed up by washing your face once or twice. You can buy special makeup removers but I find olive oil to be my favourite. (Soak a tissue with oil, dab it on your face, let it sit for a few minutes, then wipe. Continue until you can wipe your face clean. Then wash.) Baby oil and Vaseline work too but are mainly made of mineral oil/petroleum and that's not very healthy.
These are some good sites for makeup reviews.
Makeup Alley (Makeupalley - Street Smart Beauty - Homepage
Total Beauty (Beauty Tips, Product Reviews, and News from Total Beauty
Remember that you use makeup to enhance your natural features so never use more than you need. If you have nice skin, you can skip foundation and just go for a tinted moisturiser. Less is more. Always start with a little product and build it up gradually IF NEEDED.