Personally, I don’t think picking your ideal foundation is about finding the one, because as soon as the weather changes boom so does your skin and your needs. However working on a beauty counter has given me some tips that I am happy to share.

If you are buying for everyday wear, perhaps keep the coverage a little lighter or go for a tinted moisturiser and then use concealers to target any areas in need of extra coverage. Typically, this is the butterfly area of the face, T Zone, chin, and parts of the cheeks.
Choose three shades you think are a close match, swiping all three side-by-side down your cheek towards your jawline. The shade that sort of disappears, wins. This is for the days you don’t wear tan. For evening ramp it up a shade if you are a tanimal.
Step outside and check the shade in natural light.
Have a foundation for when you are tanned (even if it is fake tan!), and one for when you go weeks without sun. For me these are the daytime and night-time versions of the same one for work.
If you have oily skin, try prolonging the wear of your foundation by setting with a lightweight powder or using a primer that is for oily skin, usually these contain silicone.
If your foundation is applying streaky it could be the tool. Not all foundations apply well with brush so ditch your brush and try using a beauty blender which will produce a more diffused finish.
If it is a liquid, cream or gel, then use patting motions to push it into the skin.
Happy Humpday x