Whatever you interest there are many uses for Bondage that come from a long history of human endeavors. Bondage can bring great joy and enhance one's relationship by building levels of trust not found elsewhere.

Bondage may be used for:

to keep someone in a special position,
to limit somebody's ability to move,
to stress the feeling of helplessness and powerlessness,
to limit someone physically by the pressure of the used materials,
and as an erotic art 

Bondage can be very enjoyable but it is necessary to have a little knowledge of physiology, materials, and techniques.
The partner's safety must always be priority one and before starting a bondage scene, you should ask yourself if you are able to grant your partner's physical and mental intactness at any time.

Safety
Blood circulation, Nerves and the Respiratory System
Essentially one should be careful with those parts of the human body where nerves, sinews or blood vessels can be found directly beneath the skin. Critical places are the inner side of wrists, ankles, elbows and knees. Intense or long lasting pressure to those spots can cause severe problems, such as build-ups of blood or damage in the nervous system. First signs are numbness, feeling of cold or blue-colored joints.
The active partner should always keep an eye on the passive and check for such signs. If it seems to be necessary you have to loosen the bondage and massage the affected limbs. If the feeling of numbness does not disappear within two days, see a doctor.
Never put a rope around the neck, as breathing must always be possible. If you put ropes around the chest, take care that the passive is able to breathe without difficulty.

Joints & Muscles
If fixing somebody, esp. in a suspension bondage, make sure that the tension is distributed equally. Strong traction in joints or limbs can cause severe fractures in bones or muscles, especially if the passive should happen to faint.

Supervision
Never leave someone who is unable to move alone, for the passive needs your intense care as he is exposed in a state of helplessness. Problems with the blood circulation or the respiration, fainting or even a clumsy movement or stumbling can result in serious problems. Use a safeword to make sure that the passive is able to give you feedback if there are problems.

Releasing
There are situations you need to loosen a bondage immediately.
Having a belt cutter, knife or scissors close by is very useful and you should never hesitate to cut the ropes as those do not cost a fortune. Your partner's health is most valuable and a rope doesn't cost much compared to your partner's health. Bandage scissors  are very useful and easy to use since their tips are rounded and you can not accidentally hurt the skin.
If fixing someone on hooks in the ceiling or something comparable use special "panic hooks" (those can be opened even if you put a great deal of weight on them) which can be found in stores that sell equipment for horseback riding.


Summary
Always make sure the person is always able to breathe freely
Never put ropes around the front of the neck
Never squeeze nerves
Never leave a bound person alone without somebody watching
Agree on a safeword
Make sure you are able to loosen the bondage quickly
Never bind someone face downwards onto a soft ground (danger of suffocation)

Much of these ideas I borrowed from other sources on the subject. These are the ones I found most important and have listed them to help those who are new to the arena of Bondage. Remember that above all BE SAFE!!!!!!