A tripod is a must when photographing any waterfall. Unfortunately, the viewing platform for Mingo Falls is a small wooden bridge. As people walk on it, it shakes, ruining any chance for a steady shot.
We got lucky on our last visit as there was only one other couple. I just waited until they finished, then had the bridge to myself for a bit.
We have seen people climb below the bridge to get photos, which seemed to work for them.
As for lighting, the top of the waterfall can get very bright. The light also doesn’t evenly extend to the lower half of the falls. If you have a graduated neutral density filter, this may be a good time to pull it out.