Many people who would like to work their dogs don't know where to start, this section is meant for people just looking to start or novices. Gundog Training, where do I start by Pippa Mattinson is a great article to read, her Happy Puppy Handbook and Total Recall books are a must have.
Find a Trainer - This is the first step for someone new to it all, serious gun dog training starts at around a year of age, however, foundation puppy training takes place earlier. Gun Dog Training is completely different to obedience training etc, so go for a trainer who actually does training for gun dogs. To find a local trainer, try The Gun Dog Club website, this website is packed full of information and well worth a visit! I started my first 'gun dog' myself, I thought she was fantastically trained, but quickly realised I had inadvertantly trained into her several bad habits. In the words of my trainer "It's not what you train them, it's how you train them". A good trainer is most definately the first and most important thing to do.
There is a page on Facebook which is a friendly community of people all of different levels of training where you can ask questions and/or help others if you are more experienced: Gun Dog Training For Novices
There is a huge amount of information out there about training, my advice would be to look at as much as possible. There will be different opinions on when is best to start training and how to go about training. I always start playing with my pups using a ball from day one, this builds up good foundations for retrieving and because it is only play, I feel it's a gentle way to start and helps form a good bond, but steadyness to the throw comes a lot later.
Here is an informative piece on what age to start training.
A good bond with your dog is imperitive and the only way to start, you and your dog will be a team in the field and he/she will need to trust your commands/instructions and you will need to trust that they can follow them.
You will also need the tools of the trade, as it were: dummies, whistle and a long line amongst other things. These can be found online, your trainer will no doubt recommend which ones you get, the basics are very reasonably priced.
A good 'sit' and 'sit, stay' are very important as is a good 'heel' when it comes to field work, training sessions should only be around 10 minutes in the beginning when they are young, you don't want your pup to get bored and lose interest.
Your dog will eventually need to become accustomed to the sound of a gun, this should be done slowly working from a distance to the sound and steadily moving closer to it so as not to scare your dog, you can discuss this with your trainer when your dog is ready.
Once your dog is ready to work, call around local farms and ask if it's possible for you to go 'beating', this is a good way to get you and your dog accustomed to the field, guns and the whole working environment. If they see that you are a good team and you have a well trained steady dog, you may be invited to start picking up.
You can also join the National Organisation of Beaters and Pickers Up to find shoots and contacts. They also have a Facebook page
There is also a Beaters and Pickers Up page on Facebook.
If you would like to compete when your dog is ready, The Kennel Club website will give you details on Field Trials.
There are other non competitive awards for you to earn, The Gundog Club 'Field Test' certificates have different levels for the different types of gundogs (retriever, spaniel and HPR) see The Gundog Club website for more information.
Good luck and enjoy!