Although it's important to replace your running shoes when they are worn out, you also want to keep them performing their best for as long as possible.
Only wear your running shoes for running: It may seem obvious but it's worth noting - the more you wear your running shoes for things other than running the quicker they will wear out.
Remove your shoes properly: Make sure you're always fully undoing your laces when removing your shoes. Using the other foot to slip them off the back of your heel will break down the heel counter and overstretch your shoes.
Keep your shoes clean and dry: Give them a quick clean after every run and remove any stones from from the tread. If they get wet leave them out to air dry before packing them away. Don't wash or dry your running shoes in a machine, and don't dry them on a radiator, as this could damage the materials and glue.
Rotate your shoes: If you are a regular runner you may find a benefit from having a couple of pairs of shoes on the go. Having a running shoe rotation gives your shoes time to decompress and fully dry out between runs. Having a rotation also means you can wear the right shoes based on the weather, the terrain you are running on, and the speed you are running at.