The #1 most important thing a person can do to ensure years of use from their bow, is to take care of the string. The strings and cables on the market today are very advanced and durable, but without care, they are no better than the strings of the medieval archer.
The first and easiest way to take care of your string is to wax it. Wax is cheap and easy to obtain. The string should be waxed every month in the off season and every 2 weeks during season. Shooting and the elements take a toll.
Make sure you check your string every few months for wear. Check not only the nocking point, but also the serving around your cams. If you are using a metal D loop, check this area more often.
In the off season, it is not necessary to back your poundage down. Keep your bow in a case, not hanging on a nail or screw. This will cause damage to your string. Use only approved oil on your cams. Products like W-D40 will also damage strings.
Strings should be changed every 2 years. With proper care, they will last this long, or even longer.
Wax your string, check for wear, properly store in the off season, and your bow will not end up like the poor bow in this picture.