Add an arbor to one side of your house. Plant flowering, creeping plants such as clematis on your arbor. Flowering plants will make the boundaries of your house appear wider. Nurture the plants according to their instructions, so they develop fully and cover the entire arbor.
Plant a variety of foundation plants in front of your house, extending into your front yard, to give the appearance that your house is wider at the base than it really is. Sculpt your foundation plants into bulbous plant shapes, rather than narrow, long shapes that might reinforce the height and narrowness of the house behind them. Rounded plants such as burning bush, holly and hydrangea are all good for this purpose.
Extend your foundation landscaping to the sides of the house to give the house a fuller and wider overall appearance. Use smaller and smaller foundation plants as you get farther away from the house to create a graceful, curving line of plants that leads up to the house itself.
Obscure the actual line of your house with evergreen shrubs at each edge of the house. Plant two or three evergreens at each front corner of your house.
Give your house a richly decorated side yard on both visible sides. Use the same creeping plants on your side yard fences as you used on your arbor.