All of the dogs I have ever owned have learned differently, but my approach is always the same. I use posative reinforcement with the smell (such as a hide or carcass) of the game I want the dog to hunt at a very young age (3 months). I then just allow the dog to tag along with me when hunting for the first year of his life, continuing to keep him familiar with the smell by playing with hides and putting him around as many dead game animals as possible.
By 1 year old, the dog should be showing a big motivation to hunt and should really start singling out the game that you want him to chase. I do not use shock collars to break dogs from trash, rather I just force the game that I want them to chase on them.
I have always been very leary of encouraging a dog to chase non-game animals, as I feel it will distract him from focusing on the most important animal (whatever that may be).
My newest deer dog I got this year had located and tracked 6 crippled or dead deer before his 5 month birthday. I truely believe that the most important thing in making a good hunting dog is communiacating to the dog what you want him to do. Dogs strive to please their masters so much, that once you get them focused on the task that you want them to do, they will almost always excell at that task.