If you don't want to spend lots of money on decorations, here is a great way to decor your wall with the designs that you like.
All you need is some stationary tools that's available at everyone's home;
A construction paper, pen to draw with, and a sizzer to cut the shape.
If the paper's color is as you desire its great but if not that's not a problem.
You can color the paper, i colored mine with a water color pallet
Draw the shape that you want on the construction paper with the pen. Then, cut the shape with the sizzer. If you want to color the paper now you can do so.
Now that you are done, all you need to do is sticking the shapes to the wall
Use a double sided adhesive tape
If you are not sure what design you want to make with the shapes, you can first stick them with a normal tape to the wall then exchange them with the double sided tape.
I made this for my bedroom's wall.
Here are some other ideas