Most village horticultural shows are judged to RHS standards - setting the standards and providing local judges etc is part of the work of the RHS.
Have you ever been to the show in previous years? That'll give you a bit of an idea - but if it's anything like the village show that I used to enter there'll be some people who've been showing for years and they g row things especially for the show and their exhibits look amazing, and then there's everyone else who enters the best they've got in any given season.
My best advice is to get hold of the entry form and study the requirements - for instance if it says 3 pompom dahlias don't enter 3 cactus dahlias. There are also recognised ways of presenting the exhibits, so if I were you I'd ask the Club Secretary for guidance - if they've got any sense at all they'll welcome new interest and be all kind and lovely to you.
Then when you're at the show look and see who's done well and congratulate them and if you've any queries about why you've not got a First in all classes, ask them - most people love sharing their knowledge
Many many years ago I won a First with my Purple Sprouting Broccoli, simply because the winter weather had been so bad most people's had almost died, so they'd pulled them up - I think mine was the only allotment with any broccoli on it, and when the weather had picked up we'd got some fresh growth - I picked it, exhibited it and won
Give it a go and let us know how you get on Good luck!