Celestine has some really good ideas and points.
My system is far from perfect, which reflects the complexity of archiving photos from a variety of branches of a family and from a variety of sources.
Some of mine are simply named with numbers, some as Celestine has suggested, especially when I know the year. If I at least know the decade, it begins with eg. 1950s_xxx.jpg
As far as folders, that's what I rely on when trying to find a particular photo and keep them separated and organized. Each branch of my family tree has a separate folder. Each person for which I have tons of photos has a separate folder, or multiple separate folders.
Examples: Cheri childhood, Cheri High School, Cheri 4-H, Mom (I put her name instead of mom so it will make sense to others) childhood, Mills family, Chester family, within the Chester family, there is a separate folder for Edrie, since there are more photos of her.
For photos that have a story, or a lot of people in them, there is a document with the same name as the photo where I can type that out. I have also sometimes saved two versions of the photo - the original scan, and a copy that has the people identified by typing in the edge in photoshop.