Install a new spark plug, fill the tank with fuel and check for a kink in your fuel line if your gas trimmer won't start.
Clean or replace the trimmer's air filter as well as the plug if it won't accelerate or lacks power when you need it.
Adjust the choke and clean out your air filter if the trimmer smokes during use. Empty the gas tank and refill it for another option.
Inspect the cord for breaks or cuts and ensure that the extension is plugged into a proper socket if your electric trimmer will not run properly.