I'm far from an expert on Stonehenge but I can say that the time I visited it was very frustrating trying to get a good classic shot of Stonehenge because there's all your fellow visitors there wandering around too (in June the allocated spaces were full), cermemonies going on and security in luminous jackets. I definitely found that the time was much too short for exploring and getting good photos, plus the sunset was pretty dull with no clouds except right on the horizon where I didn't want them!

In the end I tried a handful of setups and then just wandered around.

Morning might be better, I was scrambling to catch the last light and most of the shots were dissapointing. If I were to go again I'd do an early weekday morning in winter and hope that there's only a few fellow tourists.

Others would give you better ideas for details to look for but I think it would pay to be well prepared, I definitely wasn't and ended up getting frustrated.