Cockers are not busy or merry, they are nuts. So, when someone tells you that they are demented bumblebees, listen.
Gundog manuals only go so far. No matter how many you read they never seem to cover the exact issues raised by your particular dog. They can be useful, though, for flinging at a dog that is running-in.
Be aware of the difference between the hunting and retrieving breeds. Try as hard as you can to hold off buying a puppy until you have a good idea of how the different breeds work and which will suit you.
Ask for advice. It will probably be years before you actually start taking it, but getting help is an essential first step towards learning.
Try not to get too serious. The first sign you are becoming a gundog anorak will be when your dog starts taking the mickey. Be aware and beware.
Even if you get to the stage of competing with or being paid to work dogs, keep hold of how much fun it is. Your day may be wet and tiring, but there will always be a nugget of pleasure in there.