I’ve never had a problem removing plugs for some reason – knock on wood – but what I’ve heard say is to use some penetrating oil, let it soak in a couple hours prior, then when the time comes to give it a go, turn the plug in the tightening direction slightly first, then hopefully it will back out. Pretty much everyone agrees some kind of impacting air wrench with a socket that won’t deform is the best tool combo. Knocking on a ratchet with a hammer seem like it would be better than nothing anyway. Sort of a poor man’s impact wrench. I think it might work better if you used a 1/2 inch drive, and not a ratchet but just a breaker bar for that. But still probably not as good as an impacting wrench, even if you manage to not hit your thumb. Or the fuel pressure regulator! If I had a problem where a plug wouldn’t back out with the engine cold, I’d probably run the engine a while and let it heat up then try it again.
I think one reason why I’ve never had the plug removal problem is I always put a little dab of moly-lube on the threads during the install. Most folks here seem to prefer a product called “anti-seize” rather than using moly-lube. Since the folks here are mostly pros, and I’m just a driveway diy’er, theirs is the advice I’d go with.
BTW, one of the most recent issues of Popular Mechanics magazine has an article on ideas how to remove stuck fasteners, including spark plugs.