I'd like to digress slightly (since I obviously can't help with the precise topic). I also used to have an FA qualification, so here's a few things you might find useful.
Most importantly; did you use a Fox 40? Tornado? Something else pealess? Don't do that. Having said that I'm not at all convinced by these huge wide-mouth Thunderers that the entire rugby world is in love with. They sound beautiful if you're about 5 yards away, but unless you're gonna blow the pea out for everything, I've not seen a referee yet who used one of them and didn't have problems with getting attention in the heat of the moment. The little 660 is the one you want.
Staying on whistles; your ball out of play whistle can be used for that and other minor stoppages, your old free-kick whistle is now your penalty (or other "major stoppage") whistle, and experiment a bit to find something that sounds reasonably long and happy for tries.
Read
this thread and make sure it's been properly digested. The 10m law is your friend, you use it if any of the minor chirping starts, the stuff that used to annoy you but you'd think "I can't book him for that, it's too soft". Now you can do something about it!
Most captains will actually behave like team captains and not like another lout with an armband. You can and should use them to your advantage; if he says to you "just bring any problems to me and I'll sort them", there's a better-than-even chance that he might actually mean it. Call time off and warn him before you bin anyone for persistent infringement. A lot of the time this will sort the problem for you, and if it doesn't, being able to say "I told you so" ends any possibility of argument.
Cards; remember how you got told about the FA's extremely formal procedure for giving them, and probably ignored most of it after half a dozen matches? You want to go back there now. You've probably got a teamsheet so you don't need to worry about getting a name; but you call the player and skipper in, explain to the captain what the offence is, then what the sanction is, then put the card up. This doesn't have to be a speech, though, and because rugby is an enlightened sport they give referees microphones so you can hear examples of good practice from the professional game.
Finally, running your diagonal will get you funny looks, as will asking club linesmen to flag for offside... ;-)