Akash Hamirwasia shares some good suggestions for activities that will help you improve your skills.
As every Blender user spends most of their time inside a computer, here are hobbies that every 3D (not only Blender) artist should have. These hobbies not only refresh you once you are done in Blender, but also allow you to explore things that you will find it useful in your 3D Future.
1) Photography: This is pretty common, and extremely useful. Even if you don't have any professional cameras or equipment, every artist should try to at-least capture a nice picture every week. This not only improves your skills of selecting proper locations for photographing, it also allows you to understand lighting, composition and even more that would be seriously helpful and inspiring when you comeback to your computer again. Whether you are capturing some Nature scene, or just a part of your table, try to make it as spacious as you can.
2) Drawing: This might sound boring, as most of us used to do it when we were kids. But you should always practice drawing. There's always a concept created on paper, before it is actually done in the computer. It doesn't matter if you don't have professional software, just use pen and paper, or any other tool at hand. Drawing essentially brings out your idea, and is easy to customize till you bring it to the computer. It also teaches you how to properly layout your scene, to get the most out of it.
3) Keep Exploring: While this is not a proper hobby, Exploring is one of the biggest key to get inspired for your next artwork. Some people might suggest you to just go through stock images online, what I would suggest you is to spend some time in your local surroundings too. This not only refreshes your mind, but also gives you ideas when you go back to your computer. Keeping yourself inspired is extremely important, whenever you are in the middle of a project. As I have seen many people(including me!) that they just leave their project in the middle, and never complete it. Get ideas, and keep yourself inspired and this will allow you to give your render a unique taste.
So those are all some small hobbies that I would recommend a 3D artist to follow. Again if you find any of them useful, I will be really glad. Even if you don't want to inculcate any of those hobbies I mentioned, just remember one thing: "You Need to Just be Creative!"