Word of mouth is probably the best way to find a good training class - preferably with someone who's had dogs before and has been to more than one as they'll have greater experience of what's out there.
- What did they enjoy about the class?
- Did they find the instructor friendly and welcoming?
- Would you be able to observe a class before taking part with your dog?
- Were other members of the class keen to chat and discuss their dogs?
- Was it a quiet environment or were there lots of dogs barking?
- Were there lots of happy tails with dogs seeming eager to join in with the training activities?
- Where did they train? Where provisions made for the dogs comfort such as rubber matting protecting soft paws on a slippy floor?
- How many people did the instructor have in the group?
- How well-trained does the dog that's been to these classes appear to you? Note you're not looking for a perfectly behaved dog - but one that does seem to listen when asked to and can respond to a few cues such as Sit, Down, Come.
You might find recommendations through friends and family, your local vets, your groomers (if applicable) or in the local pet shop.
In fact you're more than likely to meet someone whilst out dog walking who'll stand and chat to you about what they recommend - dog people are generally friendly, helpful folk :)
Association of Pet Dog Trainers, APDT
I'm a member of the APDT which is an organisation of dog trainers who have to pass an assessment in order to join. I did this as I felt it was important that before I appeared on their website, that someone had assessed what sort of training qualifications I had and what sort of lessons I could provide to members of the public.
There are other organisations that dog trainers can join, but check them out online before picking up the phone - you can find out a lot through internet research about the sort of training they offer and whether they prefer positive reinforcement methods or outdated punishment :(
A Google search will bring you up a list of local names if you can't find someone from the APDT who is local to you, and I would suggest ringing around a few to get a feel for what sort of training is on offer.
For example my training classes offer a block of lessons as I have a structured plan to work through to help you achieve your dog training goals, If you're just turning up adhoc the instructor won't necessarily be able to help with them.
Plus do they run any sort of assessment scheme such as the Kennel Club's Good Citizen dog training scheme? This gives you a clear indication of the sort of training you'll be working towards. By talking to a trainer and asking some of the questions above, including planning a visit to one of their classes, will give you a good idea of how welcoming and helpful the training environment will be.
Remember you'll be learning new skills alongside your dog and you want a positive and encouraging environment for yourself as much as for you dog :)