When you‘re bored of smooth and simple walls and you don‘t want to glue wallpapers, you can always paint it with geometrical shapes. The room will gain dynamics and when you get bored of this solution you can always repaint everything.
The wall of geometrical shapes looks particularly nice in the children‘s room and it‘s very easy to make it. You can separate different colours with strips which can be made when you stick the wall with a painting tape. When you have painted the wall and the paint dries up, you remove the strips and you have spaces between geometrical shapes.
I‘m writing writing and seeing that I haven‘t saved any example with stripes. Probably I didn‘t like it so much but I‘ll place the one at the bottom.
You can avoid making spaces and join different colors in a simple way. Of course, painting would also be helpful for that (but firstly please wait until the place where you're going to glue tape will be completely dry).
Similar colors and shades look most beautiful and gentle. Contrasting colors can get bored faster and look too bright but it's the taste of each separately. It's also best to choose the shapes that take larger area. Indeed, you don't need any artistic ability for that - you can get any broken forms.