What's a good routine for a teen with oily/acne prone skin?

It's great to establish a skincare routine in your teens/early 20's. If you're just starting to get a little oiliness and occasional pimple I would suggest skincare that is non-comedogenic and non-oily as this could aggravate acne otherwise.

In the morning, protect your skin from oxidative damage. Apply a hyaluronic acid serum with Vitamin B for immune protection as that will provide hydration without oiliness and then apply a non-oily broad spectrum SPF15 day cream.

At night, start introducing active skincare slowly. Apply Vitamin A formula, starting 1-2 times a week and increasing to daily application. If you experience sensitivity then add in a keratolytic (AHA & BHA cream) next, such as the Purity Smoothing Serum. If you experience severe acne you can book an appointment for prescriptive medication topically or orally.