I just set it on the strut mount near the coil, use the rubber to hold it in place near a bolt, you want no more than about 1/4" gap from the metal electrode to the body ground (like the bolt for the strut). This is just to give the spark somewhere to go, and its a good way to see if the ignition is working while cranking the engine.
the main thing is to get clean fuel to in and oil pressure/prelube for the cam and pistons. If the fuel is question at all you really should just pull the tank and start there. You can chase a lot of issues that will ultimately go back to poor fuel if you don't get that handled.
Dropping the tank, getting is cleaned out and sealed if needed is a good start. Some radiator shops will do this service. Its a good idea, unless for some reason the tank looks good inside and the fuel that comes out is nice and clean (not likely). Note some tanks will have so much rust in them that they will have pin hole leaks, all this must be addressed before getting the car out on the road.
Speaking of which you will need to service the brakes and clutch as well, they will have rust in them and prob have to replace at least the brake and clutch master cylinder and prob rebuild the rest (front calipers/ rear drums cylinder/clutch slave cylinder). So have that planned once you get the engine running. Don't want to take off and find out the brakes don't work.
You really need to just consider EVERY system and realize they all likely will need attention engine/brakes/cooling/suspension, all suffer from age and lack of use.