How to decorate too much colorful wallpaper?

With some molding strips, you could create some large rectangular panels in the walls and paint these panels a neutral color. This would break up the floral design and perhaps then you could hang pictures or a mirror inside the panels.

Add some pillows on the sofa with a couple of the colors you like most that are in the wallpaper. Also as M.M. said, adding a couple of large mirrors would reflect the other side of the room which might tone down the "busyness" of the paper. Actually, it looks quite happy...so make the most of it. Perhaps some dark navy pillows and yellow ones will draw the colors further into the room. Maybe some yellow flowers on the dining room table.

Depending on the type of wallpaper you have, you could make a glaze with paint and water. Then you can brush or or tag it over the wallpaper to tone down the colors. Be sure to use a color that will compliment the color of your room. You can use acrylic or latex , try on a small area where it will not be seen

Sometimes a mistake is just a mistake and you have to accept it and move on. Since it’s only one wall, how tough would it be to start over? If you hate it, you probably always will. Worst case scenario, paint over it if you must. Far better to remove it.

Me again! some very wide, but not ornate frames would also help break up the floral, like a dark royal blue frame, three inches wide for a picture or mirror. No thin lightly colored frames or metallics. Gold frames are going to make this too old-ladyish unless they are very modern, and over-the-top in their width. I would avoid multi-colored, floral or very busy images for your pictures as it will confuse the eye. Perhaps large, widely matted black and white photos? I love the colors in the wall paper, it's a very bold choice-hooray! You'll get there with your full room! Get some fuchsia, royal blue or golden yellow in the room, most stores let us return things that don't work! stay away from earth tones, use saturated rich colors, nothing muddy. Maybe consider a slip cover for your sofa?

To make it look intentional, use a few of the colors in the paper as décor such as pillows, drapes, decor and rug. Sprinkle the colors you choose around the room, it will help tie the wallpaper into the whole room. I would stay mostly with solids, not prints. If the wallpaper is on more than one wall, you may want to consider taking some down, and just leave it on a feature wall.

You could try adding Chair railing and below that create some oblong areas made with molding then finish with a paint that's in the wallpaper colors in the area and paint the molding a nice neutral color.

Take 1 step at a time: Many great ideas above, go slow , the paper is rather busy, the idea of adding colors from the wallpaper to couch pillows is great, get a plain table cloth for your table that coordinates with the paper, put in a new coordinating rug under your coffee table, live with that for awhile, if still not happy, take off the paper and paint the wall.

I'd do a chair rail around the bottom of the room, if removing the paper isn't an option.