An obvious place to begin is with color. One trick of the trade many designers use it to pull an accent color from the rug, window treatments, or upholstery to work into artwork on the walls. In this way, everything in the room is subtly unified, even if you're layering with lots of patterns or experimenting with several different hues at once. Try purple wall art that speaks to the sheer curtains on the windows; violet poppies make this warm shade sing, especially when the floral plaques themselves are placed on an opposite wall.
Artwork can make or break the overall look of a room, so it's important to choose the right piece! You've got many factors to consider when choosing your new wall art: should it be silver and gray or vibrant and multicolor? Wooden or metal? Matte or shiny? By taking these options into account—and doing a thorough survey of the other decorations in the space—you're one step closer to finding that pivotal piece!