Exhausts are a hard thing to prolong the life of, however the best things to do are avoid deep puddles and employ steady acceleration and braking which help reduce the vibration in the exhaust. Stop start journeys are the worst type for an exhaust as the gasses cool and condense into liquid acid that corrodes the exhaust from the inside out. The things to look for with your exhaust are a rumbling noise, sometimes a knocking or banging noise can also be heard if the hangers have corroded and they are no longer fully supporting the exhaust.
These images show a corroded exhaust where the black box had actually fallen off.
After the exhaust had been replaced by one of our trained mechanics.