Greenhouses are well known as a way to protect plants during severe weather, but they can also be incorporated into the existing landscape in a meaningful and useful way. The more accessible your greenhouse, the more use and enjoyment you'll get out of it. The better it is situated (both inside and out) for optimal plant growth, the further your investment of time and money will go.
In most of the United States, it makes sense to extend a greenhouse from a south- or southwest-facing wall. This location offers the greenhouse protection from north winds and the heat bank of the wall of a building while exposing it to the longest growing hours. But in the southernmost states, it may make more sense to extend the greenhouse from an eastern wall. The heat of the sun through glass can sometimes build up to well over 100 degrees Fahrenheit in the South and will cook your plants (and you!) during the summer. Morning sun is less hot, and fewer cooling mechanisms will be needed during summer.
A greenhouse built over a large enough land area can be landscaped. Mounds can situate plants with low water requirements above moisture-loving plants. If it is tall enough, an orchard of miniature fruit trees may be grown inside with year-round herbs growing beneath them. Transplants and temporary greenhouse "residents" can be set on suspended shelves or hung above the permanent garden until it's warm enough to move them back out again.
Ponds inside greenhouses keep fish and other aquatic life active for a much longer season, if not year-round. The pond should be installed before anything else is planted. If it takes up a large enough area, you may even consider building a small bridge over it so that you can easily access more areas of your greenhouse. The addition of water features helps moderate extreme temperatures and increases the humidity inside the greenhouse.
Outside the Greenhouse
Greenhouses are kept warm through the winter passively by solar heat, so if there is a tree or building blocking sunlight for most of the day during the winter, your greenhouse will have a harder time keeping warm. If a west- or even east-facing wall gets more sunlight, consider building your greenhouse there. Accessibility is also key. If the greenhouse has a door leading directly from the house, you will lose less heat each time you access the greenhouse, and the greenhouse will also insulate your home.
Since greenhouses often have clear walls, consider the view into your greenhouse as well as the outside view from inside your greenhouse. Landscaping outside of the greenhouse should not block the light of the plants inside -- unless they are shade-loving -- but instead should complement the themes inside. Likewise, the walls of the greenhouse should not be treated as mere storage areas. Make sure it's your plants that are on display; tuck your tools and materials in a shady spot where they'll keep better and last longer.