Bedrooms are a sanctuary and as such, they should feel good to be in. Since you spend a lot of time in your bedroom, it makes sense to me to invest enough effort into making it a space you enjoy.
All the IKEA catalogues of beautiful, stylish rooms only look that good because nobody lives there. There is no mess in those photos, because there are no belongings. You could take this as a hint to declutter which is a good shout but given that most of us are pretty keen materialists, I would consider this a sign to give up on a sleek, minimalist aesthetic and embrace reality.
Get photos printed for free here and here and here and here when you sign up. Pick up free magazines and cut out the pictures you like. Instead of making a scrapbook or putting together moodboards, use the space on your walls. This way you get to look at your fave pics all the time, instead of hiding them away on a shelf. Every time you turn on the TV or leave the house, you are bombarded with thousands of images designed to undermine your confidence. In the words of this See Red Women’s Workshop poster, don’t let them into your homes!
In your room you can recharge and you can help yourself by surrounding yourself with positive images that affirm your identity and inspire you, or at the very least, don’t make you feel like shit.
Decorating the walls will boost your creativity; as an exercise it destroys your fear of the blank page because you know you can change it all around again if you change your style or your mind. You have the time and space to do all this, so it’s no pressure. To some people it will just feel like sticking things on the wall, but to me it sometimes feels like curating my own gallery and other times working on one big collage. From my perspective, you can explore your creativity this way without having to learn new skills.
Once you have worked on your room and if you are feeling bold, you can break out and start decorating the streets. If you want inspiration on street art and subvertising, check out See Red, Brandalism, Stop Telling Women To Smile, etc.
You can often find good furniture in your area for free on Freecycle, a project which reduces waste by sharing. I’ve got a bookshelf, picture frames, posters, a mannequin torso and other stuff from here before.