I'm going to push against the grain here. One of my friends first suggestion anytime any of my outboards gives grief starting, his first and usually only suggestion is "change the spark plugs!" I cringe!
Most small outboards use a magneto ignition which is one of the oldest most reliable ignition systems. Even my old Kohler 7.5KW generator
uses a magneto. And again my friend has even suggested "change the plugs" on that when the problem was a defective fuel pump
that I took apart and repaired. I loath changing spark plugs. Clean them yes on occasions. Gap! A good gap is something around .025" that I make using my eye for measuring. I find it just isn't critical!
OK, I know I have just opened a pot of poop, I cannot however go with the "just change the plug" gang