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You have 3 or 4 "rooms" there - the lawn, lower patio, higher patio and possibly the odd little bit at the side (I can't really see what is there as it is blurry). The back of the house feels quite modern so you could pick any style you want. What style do you like? Tropical, Mediterranean, cottage, architectural, formal, Japanese, an edible garden, a fragrant garden? You will definitely need an irrigation system or at least self watering planters if you want an easy life...
I would make one patio a dining area, and one a sitting area (unless you need a play area for young DC?). I think you need a focal point at the end of the garden - a large tree or shrub in a planter, seating area, water feature, bird bath, garden mirror, decorative wall, lighting etc. I would do the same with the little odd side area, create a focal point. I would divide the 2 patios into separate feeling spaces too - either with a pergola, plants to create an "entrance" on the steps eg a box ball "hedge" with 2 standards to create a "gate" or planters with different height plants in a curve, if you want a softer feel. Climbers on the fences and over the shed/garage, to soften the edges. If you paint the fence a dark colour and have climbers with dark foliage, then plants with light foliage in front, it will create an optical illusion of space.
Step 1 - decide the style/colours you like and how you would like to use each "room" in the garden 
Step 2 - come and ask the gardening board for ideas on how to achieve that and planting suggestions!