Breeding dogs is not for the faint hearted and requires a lot of knowledge and expertise, both in your chosen breed, the lines of your own dogs and in the care of bitches and puppies. Before you consider breeding you need a dog that's good enough to breed from, if you have a show cocker that's usually one which has done well in the show ring and if you have a working cocker one which is either a proven working dog or a successful field trialling dog otherwise you're not really breeding to improve the breed which should always be the main aim of a breeder. There are plenty of nice enough pet dogs out there but only dogs which are an exceptionally good example of their breed should be bred from. I'm not trying to be harsh but everybody on this forum loves the cocker breed and that is not a good enough reason to become a dog breeder. You have to genuinely know your breed and the lines of your dog and what your aims are in using your breeding programme to really improve it. You should be a member of the relevant breed club(s) and also have your puppies KC registered.
You also need to find yourself an experienced mentor, someone with experience preferably in your breed but certainly in dog breeding who can help and guide you along and provide advice etc. when you need it. You'll need to know about the relevant health tests for your breed and have these carried out on all your breeding dogs and be prepared if you do breed a litter for the time and money that it entails - health tests, stud fees, food and supplements, vet costs - scans, check ups, if the bitch needs an emergency c section these are very expensive, if the pups are ill and need treatment and of course you have to be prepared for it to go wrong as it often does and you could lose the bitch or some or all of the puppies. This can and does happen to even the most experienced breeder. You'll also have to be prepared to sleep with the bitch and pups for several weeks when they're born, have a waiting list of homes for the pups to go to so that you're not selling them via the small ads etc. and of course if at any stage in the pups' lives their owners can't keep them you need to be prepared to take them back even if it's 5 years down the line or you end up with 5 out of a litter of 6 coming back, it's what responsible breeders do.
Have a read of this thread as well...
http://www.cockersonline.co.uk/discuss/index.php?topic=3428.0