What steps must you take before checking the cylinder compression on a spark ignition petrol engine?

Before checking the cylinder compression on a spark ignition petrol engine, ensure the engine is off and cool to avoid burns. Remove the spark plugs to allow for accurate measurement and to prevent any back pressure. Disconnect the ignition system to prevent accidental starting, and fully open the throttle to allow maximum airflow during the compression test. Finally, ensure you have a compression gauge ready for accurate readings.