Only backwash when you have to and take steps to avoid putting organic materials into a filter that lead to the requirement for backwashing. Each time you backwash, you lose some of your sand. Is it a lot? Probably not but over time, it adds up. I have spoken with people who made it a habit to BW twice a day and then wondered why the sand needed to be replaced so soon. Use a skimmer sock, a leaf rake or vacuume with a leaf canister inline, etc to avoid getting more stuff in there than you have to. Our PR Jr does a nice job of removing a lot of the gunk that would end up in my filter.
BTW, I do follow the Mother Nature rule above about using that free water to do a BW if needed. Seems like there isn't ever a shortage of rain events that leave us with too much water.