Hang textured wallpaper that isn't striped over the lumpy wall if the lumps aren't too large. It can reduce the look of the lumps and make the wall a better backdrop for furniture or other items placed on the ground.
Spray interior stucco paint on the lumpy wall. Stucco is a rough, bumpy paint used to give an area texture. The texture will help minimize the look of lumps on the wall.
Look for wall art made of small, individual pieces that are hung together. Small pieces can be hung on larger lumps or on the flat surface of the wall to provide an interesting design that draws the eye away from the lumpy surface.
Suspend several curtain rods along the entire length of the wall with curtain rod holders. Hang long, floor-length panels from the rods to hide the lumpy wall and add color to your room.
Paint your own abstract design or pastoral scene on the lumpy wall and incorporate the lumps into the design. Painting your own mural on your lumpy wall will turn it from something frustrating to something treasured.