Not sure there is much to do in the backyard. You have a bunch of mature trees back there that many of us would be envious of. Plus, maintaining that will probably be work enough for you (mowing, pruning, picking up sticks, raking leaves) without adding anything extra!
Front of house is different story...some landscaping will definitely help with curb appeal. Landscape the circle inside the drive way (turn into big planter with landscaping ties?), hedges/bushes/flowers around the house, a shade tree at the corner on the property line (behind the car in the picture).
I'd focus on the front of the house.
