You might want to include what engine, and mileage in your thread
It could be a number of things: fuel( because of additives put in at the refinery or supplier, octane your running ) timing of your engine, what kind of spark plugs your running, heat range, gap, condition of your coil, cap, rotor, wires, distributer. The age of your engine ( compression ) O2 sensor, Etc., Etc.
I run standard Ngk stock plugs in my 94 171.000 mile GA !.6L. I run them 20-25k miles and when I change them out the once square edges of the spark electrodes are rounded off from normal wear, I've checked them a short time even after a replacement and have notice the wear, at which time I usually check the gap. I tend to be picky about precision on gap, torque, when installing them, and using anti-seize, I also make sure that the top screw on cap (if it has one) is tight. Check that spark plug wire makes good snap on connection, I'll also clean inside of distributer cap and rotor for any dust or buildup. My spark plugs are whitish brown, but more white on the bridge electrode. That has been pretty consistant , and I attribute that to engine wear and fuel additives that the refinery/supplier already put in the fuel before I even pumped it into the tank. I also check cleanliness of all ignition related electrical connections.
Hopefully that could give you some things to check and consider.