If you are an iPhone shooter or a point and shoot photographer you will find Stonehenge very friendly and easy to photograph. You will not be allowed up to the stones and this vantage is about as close as you will be able to get. The good news is that it is plenty close enough for good selfies or nice shots to post on Instagram (I posted a few myself).
If you are shooting with a bit more gear here are my thoughts. Take a tripod, they are allowed and even when there is plenty of light there is a reason to take one. There is plenty of space to set up and no one will push you around. A 28mm lens will get you the shot above. You will have people in your shot, and there are three ways to deal with this. First is to make them part of your image. It helps show dimensions after all. Second option is to photoshop them out. I did that in the image above.
Third, and more interesting is to take a tripod and take a shot leaving everything exactly the same. Wait for 30 seconds and take another. Do this for four or five images. Then stack them in photoshop and erase out the people. Since people move it is easy to get rid of them.
One difficult aspect of shooting Stonehenge is finding something a bit more unique. The required shot (the first one on this post) is a must but once captured you kind of fumble at a different shot. One option is to go in close so a telephoto lens will be useful. The other option is to go wide....very wide like the image below.