Open floor concepts can be tricky since the living room, kitchen, and dining room blend together. However, similar to how you need to be strategic with the size and placement of your furniture in order to keep spaces defined, you also need to be strategic with wall art.
Try to use larger pieces to define key spaces. For example, one large accent piece over the dining room table can help to define that space as the dining area. This technique also works with sofas or chairs for living rooms.
Additionally, you should try to keep your color palette throughout the shared space monochromatic. However, you can still play with accent colors - and wall art is the perfect way to do that. For example, if your palette incorporates white, blues, greens, and yellows, use blue wall art pieces for the kitchen, green pieces for the living room, and yellow pieces for the dining room. This is a fun way to define each space but still keep it cohesive.