To ensure proper operation and long life, crossbows should be maintained and adjusted properly. Safety glasses and gloves should always be worn during use to help prevent injury. Maintain a light coat of wax on the string to prevent fraying.
To increase life and reduce wear on limb tips, the tip must fit snug and be fully inserted over the ends of the limb. Some manufacturers use glue, silicone, or rubber wrap to fill the voids and ensure that the tips are free from excess vibration. A few wraps with some black tape placed between the limb tip and the limb usually does the job and increases the life of the tips.
The trigger does not usually need maintenance, but if excess moisture or dirt enters into the assembly, it should be removed and cleaned.
The scope must always be kept dry. If moisture enters the scope it will fog up and it may take a few weeks for the moisture to evaporate.
During cold weather any scope may become foggy due to the proximity the shooters face. The combination of cold, and the hunter breathing on the scope will create fog on the surface of the lens. This is similar to the condensation build up from breathing on a cold window.
I recommend the use of anti-fog on the lens closest to the hunter's eye.
To maintain spring force in the limb, most manufacturers recommend removing it during the off season and during long periods in storage. The bow may need to be re-sighted each time the string is replaced to compensate for limb and string wear.
Before hunting, the shooter should become familiar with the operation of the bow. This includes practicing at different ranges with the same type of arrows that will be used for hunting. Factors like wind and broad-head variation will affect your accuracy.
The part of the bow that the string travels along when you cock it is called the rail. Be sure that your fingers are clear of the rail before pulling the trigger. Your fingertips will be struck by the string if they get too close to the top of the rail. This will not usually cause an injury, but it is very painful.
Compensating for angular trajectory due to tree-stand elevation only comes with practice. Most shooters will hit slightly higher on the target when they are elevated off the ground because the bolt trajectory is no longer perpendicular to the force of gravity.
This site explains it very well. http://www.bowhunting.net/abc/elevated.html