When you take your lawn mower in for a tune up the lawn mower shop will replace the spark plug, change the oil, change the fuel filter, change the oil filter if your lawn has one and possibly sharpen the blade.
What I do when I tune my lawn mower up is change the oil, change the spark plug, change the air filter, change the fuel filter and sharpen the blades.
You can buy lawn mower tune up kits online or in lawn mower repair shops and easily do the lawn mower tune up yourself.
I also run my lawn mower completely out of fuel at the end of the mowing season to make sure no old gas gets into the lawn mower carburetor which causes problems.
You can also add some Stabil Fuel treatment to your lawn mowers fuel tank during storage which will prevent your fuel from going bad and turning to varnish.