Take notes at the time you take the photo, either writing in a notebook or if your camera has the voice note feature use that. I make my living from photography and if I didn't write down or voice record the details at the time of the shot I'd never be able to reconstruct the captions later. Sometimes I'll write down GPS coordinates but that's really optional. But good location descriptions can be helpful, i.e. MP 71 on Hwy 14, or Crooked River valley along Izee Paulina Road. Get people's names down, spelled correctly.