Go without the dog first time round make sure you wear waterproof clothing that will protect you from brambles (jeans won't do the job) and give you the option to either be warm or cold (you get cold standing around and warm walking around be prepared for both), take two pairs of socks with you so you don't get sore feet and wear practical shoes that don't rub your feet, if you need new ones break them in now. Cut yourself a stick of about waste height (a coppiced tree type is best) dry it out in the airing cupboard you'll need it either as support or to bash the brambles. Have a bit of a practise run, if you have a local woods to you come off the path and see how you fair going in a straight line through the undergrowth... its an eye opener
If you haven't done any gundog training there is still time go along to a local class explain what you might be doing and ask for some help with the basics. You could also go along to a clay shoot to see if he's ok with gunfire, not all dogs are its good to be prepared. Ideally if you do take him don't let him off the lead unless the keeper specifically says that its ok to do so. I've seen several dogs disappearing off into the distance after a bird as they haven't had the pretraining required but also some fabulous dogs that have taken to it like a duck to water.
The only other thing I would suggest is if you do go ask to be paired with someone who is experienced to show you the ropes most keepers will do that anyway but it does help if you have to dispatch something and are not quite sure how or wish to do so. Good luck have fun and welcome to the world of working you'll love it!!!