General maintenance procedures for keeping a Zippo in it's most effective condition.
The obvious things first:-
Use Genuine Fuel
Use Genuine Zippo Flints
If the wick looks tired, charred or stubby, use a pair of needle nose pliers or tweezers to gently pull it through by approximately half an inch (or until a clean portion of the wick is showing just below the top of the chimney) then using a pair of sharp scissors (or nail clippers), trim the dead portion of the wick off so the clean wick top is almost up to the chimney top. Finally ensure the wick is in a central position in the chimney (not angled away from the spark s sweet spot).
If the flint spring feels a little less strong than required, gently pull it a bit longer. Don't get carried away here, it doesn't take much.
Always lift the foam when refilling, and do not overfill the lighter,
After refueling a Zippo that has been either stored, or completely run dry. Put the insert back into the lighter case, add a few drops of fuel to the wick and then spark it into life. Let it burn for 5 to 10 seconds then close the lid. This will draw the fluid up the wick and save any vapour locking tendencies the lighter may suffer, (it also stops you looking like an idiot waving it around like some people suggest you do after filling).