Protect your lens?
Want your lens to last a long time? Then make sure you maintain it well. Clean it after you've shot outside or it has bumped into something. You can use a lens pen or lens cleaning set for this, for example.
You can also protect a lens by storing it or carrying it in a dedicated pouch or camera bag with protective padding inside. It's also sensible to always have a lens cap on your lens when you're not using it.