Pick up a book like "10 Minute Retriever"... You can get bumpers for about 4.45 each here
http://www.gundogsonline.com/dog-training-bumpers/plastic-dog-training-bumpers/
Your dog needs to be on a check cord so you can "reel him in" when he doesn't want to come back...
Here's some good 'free advice'-
http://www.oakhillkennel.com/library/puppy1.html
http://www.oakhillkennel.com/library/comeback.html
http://www.oakhillkennel.com/library/introbirds.html
Here's the link that all those pages are on if you think you might see something else you'd be interested in reading up on.
http://www.oakhillkennel.com/library/index.html
Main thing is to find a program (book) and stick with it!
Best of Luck,
Kim