Indeed: smartly open your wallet - observing the pauses equal to 2 beats in Quick Time - face the RSM and repeat after me, 'Help yourself, Sir'.
Corps or Regiment? Whatever - bone up on your history (for God's sake, don't miss a anniversary date if the Dinner falls on one of those, even the obscure ones), speak to the PMC, Mess Manager and the last guy who was Mr Vice. Give the announcements, any toasts and responses in a clear voice.
When called to the top table after the grown ups have left make sure that you're not too pissed: nothing less amusing than a bladdered Vice who can't tell a joke.
Mostly, enjoy it: it IS good crack - you're amongst friends (mostly), you've all got dressed up to have a hoofing good time .............so, have one.
It gets better as you work your way up the table, though, and you see the next poor buggers shit house tiles as they go through it.
Edited 'cos I've just seen the 'REME' bit in your profile: guess the chat will be Amuisng Alternators That I've Known?
Do a search, it's often asked on here and there are a lot of good and humourous replies already posted. Also do the same search on PPRuNe. You're basically expected to be a good natured ringmaster, and your main "challenge" is to keep the guys entertained for literally ten or 15 minutes while the guest of honour gets served at the bar prior to all of the animals being released from the main tables.
You'll need a few jokes and a couple of amusing stories. Tailor it to the audience though, there's no point in regaling your guests with the time you fucked a donkey up the ass in Blackpool whilst dressed as a Nun on a stag do, if your audience is Vet Corps or the Womens Institute. Keep it relevant.
For some reason, Juniors are being invited into the mess (shock horror!) for a dining out. Of course, Mr Vice is going to be selected and it's going to be one of us! I can't think of anything worse in this sort of situation and I'd really be bricking it if it was me. What advice would anyone have to a junior that may be chosen? (Apart from not going!?)