
As others have said look for clubs on agilitynet and be prepared to have to wait for some time for a place to come up unless the trainer offers one to one sessions which are generally easier to get into quickly but much more expensive.
There are several clubs in the Barnard castle area,one to one sessions in Lanchester and I have heard good things about Jaqui Tarn who is in your area.
Always go along to watch a training session before signing up to see if you like the methods used. The dogs should look keen and eager to do the exercises and never pushed or pulled through equipment. also they should be rewarded by using either food or toys and not shouted at for making mistakes.
As for preparation start by building on a reliable wait,a send on by getting the dog to run ahead for a toy or treat and teaching a left and right by tossing a toy and saying left/right.
I taught my pup to walk over a large plank of wood on the floor to get used to different surfaces,go through a tunnel that was given to me by a neighbour,kiddies play tunnel,and to walk over jumps put flat onto the grass.He did this from six months old as no jumping was involved.
Also make sure your dog is happy around other dogs and also physically in good shape by not being overweight.
Also a good and reliable recall is a priority.
I started out doing agility for a bit of fun when my husband was in Iraq,got bitten by the bug and spent the next five years competing nearly every weekend all over the country.I have cut back a bit now as said dog is now at the top level and a senior lady!
I still do shows with my chin but tend to do more breed shows now.