String & Cable Waxing
Proper string & cable maintenance is key to the longevity of your (cross)bow. Waxing the string and cables every 10 to 15 shots is recommended. Ensure that all uncoiled areas are waxed, but avoid waxing too high, as this can cause the string to slide off the cams. Note that plastic and cotton strings do not require waxing.
Pay special attention to the condition of the string, cables and cams. Strings should be replaced at least every 2 years (but preferably annually), every ~500 shots or as soon as they show signs of fraying or damage.
Archery Bow
The red lines below show where to put the wax with this model. It may differ for your model:
When waxing the string and cables, look at the texture of the string itself. The protected parts have additional 'string' wrapped around them, while the non-protected areas have the strings/cables revealed. The green arrows show protected areas, while the red arrows show the parts that would need to be waxed:
If the difference is difficult to see, feel for the difference in texture.
Crossbow
When waxing the string and cables, make sure to wax all areas that aren't protected by additional 'string'. The rail, where the string will be pulled along it, should also be waxed. Below is an example (in green) of where wax should be applied on average, but it may differ with your model:
Below is a better example of the difference between the exposed and protected string/cable. The green arrows show the protected areas: the texture is often smooth or as if a wire has been tightly rolled around it. The red arrows show the exposed areas, where it's often a twisted texture. Per model the protected and unprotected areas may differ, so make sure to have a good look at your model when you're waxing the string and cables.
Note: the rail needs to be waxed. Even though the string has additional protection in that area, the amount of friction can quickly wear down the string if it isn't waxed.
Replacement
When the string or cables show signs of wear, damage or fraying, they should be replaced. To read more about it and see examples, head on over to : Cam and Cable Replacement or Replacing crossbow or archery string