Sometimes a corner is all the room you've got for a garden and the seating to enjoy it. Luckily, there seems to be a plant for every growing condition, including tucked-away corners. The plan you draw up for your corner garden should accommodate the space, light, and terrain factors of the corner where you're planting.
Unless you're working with a large corner area, you'll need to think small. The benches should be large enough to accommodate only the number of people that can comfortably fit into the garden and enjoy it. The more room you leave open for plants, the more garden you can enjoy. Pathways to the benches should be kept to narrow mulch paths or intermittent step-stones that allow plants to grow around them.
Benches work best in areas where plants would have a hard time growing. If the corner has a tree growing in it, for example, the benches should sit around large roots that out-compete smaller garden plants. If you're going to grade the area, or move soil to have mounds or flat areas, plan for this before you plan for your pathways. Areas with the most access to sunlight are left open for the plant life, and the benches offer garden visitors reprieve in the shadier areas.
Plant Selection by Tolerance
Corner gardens, by definition, have some kind of structure that creates that corner -- usually a wall. Walls cast shade. Plants, therefore, should be chosen based on their ability to withstand however much shade they're going to be receiving. Alternately, low walls in a sunny area might bake plants due to heat reflection. This means heat-tolerant, sun-loving plants are a better choice. Plants should also be small enough or planted far away enough from the benches to avoid taking them over.
Plant Selection by Size
The plants in the plan should be spaced for their maximum size, not the size they are in the containers bought from the garden shop. Over-packing a small area with plants makes the garden look weedy. Plants that grow low to the ground work well near the path and the benches, taller plants a little further away from the walking and seating areas, and vines can grow up the walls that make up the corner of your corner garden.