There is a major shift in architectural design towards a more ecologically and environmentally friendly building. It is coming in two parts, clients are requiring energy efficiency to be built into their buildings and governments are forcing this through requiring energy efficiency certificates to be submitted with development applications.
Insulate your house/building, use cross ventilation instead of air conditioning, use natural light, solar energy systems and water management (harvesting and recycling) and reduce your carbon footprint.

Warm in Winter, cool in Summer.
The temperature stays more even throughout the day. Insulating the roof and walls will stop the transference of heat (energy) into or out of the building. It keeps heat outside during the day and inside during the night and is a very cost effective way of saving energy. In a hot climate, ventilating the roof space is very effective also.
Glass (in windows and doors) has a high heat transference rate, it readily lets heat in or out of the building. To compensate for this, shade windows from the outside, use a film on the outside of the glass to reflect heat away from the window or use blinds and curtains inside. Double glazing in also very effective in cooler climates.
Insulate the slab on ground. A barrier under the slab stops heat from getting out of the slab, floor coverings (carpets, rugs, etc.) are good at keeping the heat in the living space.

Use less energy
Use 5 or 6 star appliances. Washing machines that use less water and electricity, solar heaters for hot water, ceiling fans instead of air conditioners, these are just a few simple ways of reducing energy use.
Use a skylight or larger windows (with suitable shading or film treatments) to illuminate areas that may require a light on during the day (or even at night, a full moon will do this). Most governments now require the use of energy efficient lights which save electricity.

Generate Electricity
Use solar heaters for your hot water. Install photovoltaic cells to supplement the mains power coming into your building. If you live in a rural area, a wind powered turbine may also be an option.
Note: I do not advocate the use of storage batteries in a domestic situation because they give of a volitive poisonous gas.

Use less water.
Harvest rain water using tanks to collect and store it for use in the garden, outside taps, toilets and laundry. Greywater, water from baths, showers, hand basins and laundry (not toilets or kitchen) can be filtered and reused the same as collected rainwater
Install washing machines that use less water and electricity, dual flush toilets that use recycled water, shower heads that restrict the flow of water to keep your water use down.
In a rural situation, all household waste water can be reused on gardens, trees, lawns or some crops. Water is treated though a Household Sewerage Treatment Plant and recycled or dispersed over the site.  

Building Design.
There are several ways to use the building to reduce costs and be environmentally friendly. First and foremost, design to suit the surrounding environment. Use prevailing winds in Summer to cool the building, block the cold winds in Winter. Shade windows in summer but allow the sunlight through in Winter by using the different height of the sun in different times of the year. Design outdoor living areas so they can be used more often.
There is a current trend in parts of the world toward smaller houses. They cost less to build, use less materials and resources and cost less to maintain.

Recyclable materials/Environmentally friendly materials.
There are a range of these available now and more are added every day. They can be composite (wood and recycled plastic) timber decking or water based, low Volatile Organic Compounds (VOCs) paints or steel house frame that are 100% recyclable at the end of the buildings use.

Vegetation
Use trees to screen the building from sun and wind and create your own personal carbon sink. Plant native flora (trees, shrubs, flowers and grasses) which require less water and maintenance and are used by local wildlife. If you want to go a step further, plant a vegetable/herb garden and fruit trees so you can harvest your own food.