When you're pumping up your kite don't stick the nozzel in to hard... will stretch the valve over time and cause air to leak out and of course don't pack your kite with either the dump or inflate valve caps in... again will stretch the valve. I learned that the hard way
Not an issue with some brands.
Direct sunlight is a kite killer... all kites die a slow death in the sun
Self launching is a sure fire way to wear out your kite before it's time... depending on the launch site of course.
Examine your kite from time to time for small rips, tears, lose threads.... want to repair stuff quick so it don't get worse.