Many also have a retaining post to hold the spark plug when the mower is not being used as well as a bail bar that stops the engine when it is released. Always be certain that safety shields and deflectors are in place. Never disconnect mower safety features. They may cause some inconvenience but they can save you a trip to the hospital. Make sure that all nuts and bolts are tight.
Lawn mowers vibrate and can loosen fasteners.
Add oil and gas outdoors while the engine is cold. Wipe all spills and allow the mower to sit while residue evaporates. Adjust mower height as well. Inspect cords on electric mowers to assure they are in good condition. Always use CFCI grounded plugs for electric mowers.