after you bring your used machine home. the best thing you can do for yourself is to get a copy of the service manual.  change your oil and filter . some machines have a oil screen instead of the filter. the manual will state how to remove and drain the oil. use an oil for motorcycles or atvs. it does cost a little more.if it has dry or disk brakes or drums. pull the wheels off and inspect the rotrs, drums, pads or shoes. most newer machines have a wear indicator on the disk brake set ups. it is on the caliper. it points between a set of bars on the caliper. as the pads wear the pointer moves towards a bar. if your machine is chain drive. make sure to wash the chain with warm mild soapy water. do not power wash it. you could damge the o-rings in the chain. you must lube the chain with chain oil. either replace or clean the air filter. all the air filters need to have filter oil. this oil traps dirt and dust from entering your engine. this is very important. if you have a wasable filter MAKE SURE TO REOIL IT after you wash it. i have rebuilt 20 atv engines because a new air filter was installed without oiling it .lastely make sure everything is tight. not overtight but tight. no one needs a rim and tire to fly off at speed. handle bar bolts should be checked if you machine has aftermarket handle bars added