All I can offer is best wishes for your debut! See if there's a category for beginners at showing. If it's anything like pet shows the club running the event often provides a leaflet of guidance for exhibitors.

Probably the main things to consider are: timing the picking, conditioning the stems, transporting to the show so they arrive in excellent condition, and having a suitable display vase.

It might be useful to get some tips from your local floristry shop about how to deal with the stems so they'll hold up over the day/s of the show.

And, congratulations on being willing to be a beginner again!