i usually edit the photo (removing the bg/colouring/sharpen) then add the bg for the icon (usually a muted pastel colour) as a layer behind the first image. once i have this big sized icon then i resize it - this way you’re not making the photo fit into the icon (since this could make it blurry/not proportionate). instead you’re making the photo already be the icon if that makes sense! i usually just make it 500-400 px i hope this helps :^D