[Enright]

You simply screw it in in place of each plug in turn, and crank the engine for about 5-10 seconds. Probably best to do it without any plugs in.
Your Haynes manual should tell you what the compression ought to be, but the main thing is as long as all the readings are healthy and reasonably close, then that's fine. Good idea to remove the fuel injection fuse as you say though.