One of the most important things (in my opinion) to do before you begin building your makeup collection is to learn what your skin type is. It'll make it that much easier to choose foundations, concealers, powders and skin care.
Finding out what type of skin you have also takes a lot of trial and error. For me personally, I have combination/dry skin. My skin is super oily in my t-zone (mainly my nose), and is normal to dry on my cheeks. Up until the last year or so, I always assumed my entire face was oily because my nose was, but over time I've learned that I don't need as much coverage or powder over my cheeks or it can start to look cakey.
So how can you tell what skin type you have? A very basic version is that if your skin doesn't get too oily or dry, your skin type is normal. If your entire face becomes an oil slick after a few hours and you're prone to acne and large pores, you have oily type skin. If your skin gets oily in the t-zone and is normal or dry on your cheeks, I would say you're combination. Skin that has rosacea or reacts to skin care and makeup is sensitive. If your entire face gets tight or has dry flakes, your skin type is dry.
Some things to remember or look for when trying to learn your skin type:
1. Know the return policy of the store where you're buying products from. Drugstores, such as CVS, Walgreens and Rite Aid have a great return policy. Basically, you can return any product you don't like whether or not you've used it. If you're buying from makeup counters or high-end boutiques, ask the associate what their return policy is before you leave.
2. If you have combination skin, you may need to buy more than one product for each need. I.e., you may need to buy one lotion that mattifies your t-zone and one that hydrates your cheeks. Or look for combination products that can do both.
3. If going to Sephora or a make-up counter, get some advice from the associates. They go through trainings with their company about products, so they have more knowledge than the general consumer. Also, ask for samples of the products to try at home before you make the investment.
4. Do your research. I almost never purchase a product without looking up reviews. On Sephora's website, reviewers are asked to share their skin type. You can put more weight on the reviews that have a skin type similar to yours to decide if the product might or might not work for you.
5. Consider your climate. I live in the Northeast where winters are brutal and summers are hot and humid. You may want to have different products for different types of the year. I keep products on hand that are more moisturizing for the winter months, and lighter for the summer months.
Sometimes, you just have to try a product to find out if it works for you. If it doesn't, keep your receipts so that you can return it and try something else! Learning your skin type off the bat will help you to avoid wasting money on products that don't work for you.
That being said, there is no golden rule for this. Try some products out and have fun with it!