For an accurate result
Take the photo in daylight, ideally near a window and out of direct sun. Flash, filters and editing shift the colors in the image, and therefore shift the answer.
Remove makeup if you can, foundation especially, and keep your face visible. Wear something neutral in white, grey or black so no garment casts color onto your skin.
Three things decide which colors suit you: whether your skin has a warm or cool undertone, how light or deep your coloring is, and whether you look best in clear or soft colors. Together they point to one of twelve seasons, from light spring to deep winter.
With a color analyst in the US it usually costs around US$300, from US$98 to US$611. This test is free and gives you your season right away, with clothes that suit it. See prices from real analysts
Prefer a person? Find a colour analyst near you or online
You upload a photo and then see your face against pairs of colors. For each pair you pick the side where your skin looks more even and your eyes look clearer. You do not need to know any color theory, you only need to look.
The comparisons run from the largest difference to the smallest. First whether your coloring leans warm or cool, then whether it is clear or muted, and finally which of the twelve seasons fits best.
You get your color season and the palette that belongs to it. From there you can shop clothes and makeup already sorted into those exact shades, instead of guessing in a shop.