As Jess says find out where your nearest meet is, then make sure your horse is reasonably fit; up to doing lots of cantering and jumping and is used to varied ground conditions (you may be running over deep mud or stoney ground, or doing a fair bit of roadwork on the day so get your horse prepared for this. Drag hunting is pretty exciting for most horses so be aware your horse may get strong/ need a stronger bit. And then go and have fun, drag hunting is great so hopefully you will both love it!
Depends how far your willing to travel! The New Forest hunt is really good, they are on every tuesday and saturday in the hunting season and i think its £15 each time for an adult. All you do is find out where the meet is and turn up! Should find details of meets on www.newforestpony.com or if not then try www.nfed.co.uk