I'm not one of the old pros but I'll tell you what works for me....
It's been difficult uploading images lately but when I repeatedly can't upload an image, or it fails after putting in all my keywords, then I physically log off of FAA, close the browser window, then reopen everything and log back on. Nine times out of ten this will resolve the problem for me. If I continue to have trouble I figure FAA is having serious heartburn, give up for the night and try again the next day.