1
Set a goal and make a working copy
Decide whether the photo is for a profile, a post, a document, or another use. Open a copy in your image editor so the original remains available. Check that the subject is reasonably sharp; if it is not, a different source photo may help more than extensive editing.
2
Crop and straighten
Remove distracting edges, straighten obvious tilted lines, and leave enough room around important features. If a specific aspect ratio is required, apply it while watching what leaves the frame. Compare the crop with the uncropped photo before accepting it.
3
Adjust light and color gently
Change overall brightness only as much as needed to see the subject. Inspect bright areas for lost texture and shadows for blocked detail. Correct a noticeable color cast, then keep saturation restrained so skin, surfaces, and backgrounds still look plausible.
4
Inspect and save a separate result
Zoom in to spot halos, harsh edges, or accidental changes, then zoom out to judge the whole image. Compare your result with the original at the same size. Save an edited copy in a format appropriate to its destination, and reopen that copy to confirm it looks as expected.