My best advice to teens would be to USE SUNSCREEN…every day…on your face! ! It is the BEST thing you can do for your skin!! And my favorite is Neutrogena Ultra Sheer which feels nice, is not greasy, and has a mild scent.
The teen years are for experimenting and so it is impractical to say only buy good stuff…unless your mom is buying. Use drugstore brands to see what you like and for special occasions perhaps you'd like to use a good department store foundation but don't get caught up overspending when the inexpensive stuff will do.
If you have skin problems do see a dermatologist…they can help with teen skin and can prevent skin conditions from getting worse.
Finally the teen years are all about fitting in but don't let your girlfriends make you too conscious of your looks…or prompt you into overspending because they have bigger budgets than you might have. EXPERIMENT and FIND YOUR OWN STYLE. Once you hit college being an individual will be a REAL asset!
AND PLEAAAASE have more fun than I did as a self-conscious teen. I'm only catching up now!!