what sort of treats do you use when out in the field? When I train peoples dogs i encourage them to use really interesting treats such as pieces of frankfurters, dried liver, spam or cheese and only use them for training or when out and they need their dogs attention. they will b really interesting to your dog and help keep their focus better than plain biscuits/packet treats etc. also dont feed a dog before you walk/train it, dogs work better with a hungry tummy and it is also more confortable for them to.
and regarding the clicker, it is basicly a reinforcement tool. CLICK means ‘thats it, thats the correct behaviour’
so for example you start by asking your dog to sit, CLICK when he does (because he has displayed the correct behaviour) and then reward. this will help him learn CLICK means reward. he will be more likely to repeat the behaviour again, in order to hear the CLICK.
it sounds a bit confusing but there are great books you can get, Karen Pryor for example. and once you understand its a really useful way to train a dog.
hope this helps