Most of the time the contact area inside the cap is aluminum. This will develope a layer of oxidation that is an insulator. This can be picked off with a dull screwdriver, like picking tarter off a tooth. No deep scratches. This can be done if the cap is in good condition other wise. Clean the dust out of the cap with warm soapy water, rinse, dry and reuse.
Thats if you don't want to change it. If you do change it , replace the rotor also.
Use good fitted plug wires. I like Bosch. Use ignition silicon grease sparingly on both ends
of the plug wires. Do not over tighten the spark plugs. Make sure there are no air
leaks between the air filter and the engine. Thats all I can think of..
Be sure and mark where the wires go in the cap,at least #1.