From Nikonians Wiki - FAQs, Photo Glossary, Good Photo Locations, Help
To have good camera technique you should
- Be thoroughly familiar with the basic controls of a camera
- Be familiar with the controls and features of your specific camera
- Know how to select the right lens
- Know when and how to use a flashgun
- Know when and how to use filters, such as a polarising filter
- Know how to physically hold the camera and stand to best effect.
Holding the camera
Hold the camera in both hands, with the right hand so that the index finger naturally falls over the shutter release, and the left hand so that it supports the base of the camera and the lens. When using a longer lens, move the left hand forwards, so that it supports the lens at the point of the tripod mount, if one is present.
Tuck the arms down by your sides, rather than having them spread out.
When shooting vertically in portrait format, use the vertical shutter release if present. If not present, turn the camera by 90˚ clockwise so that the right hand comes under the camera, as this enables you to tuck your arms in. When using the vertical shutter release, turn the camera anticlockwise.
Stand with your feet shoulder width apart, with the feet at right angles to each other. Keep the knees flexing slightly rather than having them 'locked'. Have your weight over the entire foot, rather than balancing on your toes or rocking on your heels.
If you are carrying a heavy camera bag, put it down if the situation permits it.
If you can train yourself to do so, there are advantages in looking through the viewfinder with the right eye, and keeping the left eye open so that you can see the rest of the scene outside your frame.
Make use of any available solid places to rest the camera on, as this improves stability.
See also the Nikonians guide On Handholding Technique by J. Ramón Palacios 
How to carry and protect the camera
Your camera is least vulnerable when you are shooting with it, as your mind is fully on the camera. It is more vulnerable when you are carrying it, although less so if it is in a suitable camera bag. Your camera is most vulnerable when you are changing lenses, or have the lens removed for some other purpose. Sensor cleaning should only take place in a dust-free, controlled environment where you are unlikely to be disturbed. When changing a lens in the field, keep the camera facing down, and do so as far away from dust or gusts of wind as possible.
When carrying the camera, put the strap over one shoulder, not over the neck. It is better to lose the camera to a thief than to suffer a serious neck injury.
Always fit the relevant lens hood, as this goes a long way to protecting the lens.
Keep the lens cap on the lens when not shooting.
Carry your camera and other equipment in an appropriate bag or case. You may discover that a variety of bags or cases are required for different situations. For example, only a flightcase of some kind is suitable for placing in an aircraft hold, but such a case is not suitable for ordinary carrying.
Never use the camera in weather conditions for which it was not designed. High end cameras such as the Nikon D3 are weather proofed, and can be used in rain. Consumer cameras, such as the Nikon D90 will have some very limited resistance to rain, but are not weather proofed and should be kept as dry as possible.