Learning languages. I'm one of those persons that really love to learn new things about different languages and countries. For me it's not too hard to learn new languages. Now I work on my English to make it better and I learn Swedish.
Also if it's boring for you can to watch movies with subtitles, original movies are so much better.
Go to walk and breathe a fresh air. I have, at least, three reasons why it's useful for you. First, it's so good for your health. Did you know that people who breath a fresh air everyday 30 minutes live 15 years more than who don't do it. Second, that it's useful for your skin and beauty. And the last reason you can find adventures that makes your day brighter.
Sport. Running, pilates, fitness, yoga, bicycle... choose what you like more.
Try to cook something. I think it's interesting to try something to cook (and eat later:) ) and you'll make a good mood to your closest people (and yourself too).
Make a beauty day for you. If you have a free day, than make it's only for you. Do different masks, scrubs, do your nails. It'll make you fell more confident and pretty.
If you're girl, you can to try new hairstyle, makeup or create cool outfits before you will be hurry to create this.
Here are so many interesting and useful books.
Try a type of arts. Maybe do you want to draw better? You can do it.
If you have really a lot of free time, go on learning courses that you like.
I love take new photos for the blog.
Go to google events will be in your city and visit them. What's can to be better if these events are good.
And my favorite - choose a goal / dream / wish and follow it until it come true and never give up, even it's hard.
So, what do you do when you're bored?