Usually, when the P0300 or P030X shows up, it's time to change the cap-n-rotor. The cheap-o aluminum types will toss these codes more often.
Also, if you happen to side gap the plugs, these codes will happen more frequently as the plug life tends to go sooner.
My code is always P0304. #4 cylinder. The engine light will blink on-n-off every time it happens. Most of the time, this happens while above 50mph and punching the pedal to the floor to get on the expressway or to pass.
Other things that could cause these codes to happen are fuel injectors, related wiring, sensors, the PCM/ECM, ran out of gas recently, forgot to tighten the gas cap, bad gas, gas that contains aditives and higher than 10% ethanol, incorrect fuel pressure, leaking egr valve, restrictive ports, faulty coil, wires, plugs cap-n-rotor and if need be timing.