What is the best way to charge my MacBook Air to improve the lifespan of battery?

..Another aspect includes how to maintain and use the portable Mac..

Including some troubleshooting and general ideas about upkeep, etc.

• Get help with your Mac notebook battery - Apple Support

https://support.apple.com/en-us/HT204054

Don't worry about micromanaging your battery. macOS and the hardware will take core of managing it as best as possible.

Batteries are consumable items and when you don't get the amount of use on battery that you want, then replace them. Generally, for the normal user, the usefulness of the computer itself no longer meets the needs of the user before the battery becomes an issue.

Here is from Apple Battery health for all things Mac.Batteries - Maximizing Performance - Apple

Apple's charging circularity is tasked with that duty. It will take better care of your battery than attempts to micro manage it.