If you have too much spare time on your hands then learning a new skill is a great way to spend it. If you learn skills that can be applied to your work then you are making yourself more valuable to your employer and more attractive to potential employers. Skills don’t have to be work related though, you could learn painting or juggling or how to ride a unicycle, whatever you think would be fun, and it might turn out that you have a real talent for it.
The first thing I would turn to if I wanted to learn a new skill is a book on the subject. Books are not always the best to learn a skill, but what they do give you is an insight into what you can expect if you want to take up that skill, what equipment you will need, how quickly you can progress, and if you think you will like it. So you might decide to learn painting and find some good landscape painting books to find out more. In them they might say that landscapes are the hardest area of painting, which saves you spending a load of money on a full course of lessons and then really struggling.
When you do find a skill that you like the sound of and when you check the book out then you know you stand a good chance of being good at it, then you need to find someone who can teach you. You can often find lessons at a local college during the evening in a huge variety of different things from pottery to dancing to sign language, and they are cheap too. So if you fancy learning a new skill then check out some books on Amazon first, then get a brochure from your local college and find out what they offer as well.