If you have combination skin, it's best to look for a foundation that's oil-free, noncomedogenic (for those who are acne-prone), and water-based. It also just depends on what kind of combination skin you have. Combination skin can mean a lot of things—dry in certain areas and oily in your T-zone, or dehydrated skin at the deeper layers and oily on the surface. I struggle with the latter and have found it's always best to opt for a foundation that's hydrating, but noncomedogenic at the same time.
Another thing to watch out for if your combination skin is sensitive is fragrance. Most foundations don't really have it, but some do and if your skin tends to get irritated with that in a formula, it's probably best to avoid it. Makeup artists also shared a few application tips for combination skin below.