Good to see that you're looking to go about things the right way
Where to start...
Well, the first suggestion I'd make is that you find a resonsible breeder to mentor you. It sounds as though you're already well on the way to that one
The second thing is that you need to do some in-depth learning about the breed: it's history, the breed standard and what constitutes a correct boxer. Joining your nearest boxer club is a very good idea, as is getting involved in conformation showing. Dog showing is all about assessing dogs for how well they conform to the breed standard (blueprint for the breed) and, consequently, is about judging whether or not any particular specimen is good enough to be bred from. Very few people are really capable of making proper assessments of their own dogs - so it makes sense for this to be done by an unbiased expert (ie. a judge). You can take a look at the breed standards from around the world at
www.boxerworld.com/standards
The whole point of breeding pedigree dogs is to produce dogs that are as close to how they are supposed to look and behave as possible - so it's a matter of constantly trying to breed better boxers. That's why the breed standard and assessment in the show ring is so important.
And the other major consideration is health. There isn't a lot of point in producing great looking boxers with wonderful temperaments if they're going to drop dead at a young age from some genetically inheritable disease. So you need to be very aware of the diseases affecting the boxer breed, and committed to the irradication of those diseases (which can mean taking the decision not to breed a particular dog, even though you've been planning on doing so since before it was even born).
Here are a couple of links that give you some very good information. The first is all about what are not (and never will be) acceptable reasons for breeding dogs. But once you get through that, it has some good advice about how to go about doing things the right way
http://www.boxerworld.com/rescue/top6/
And there's this one:
This gives you a good overview of what you need to learn before embarking on the path of actually breeding a dog. Your breeding mentor should be invaluable in helping you to learn these things:
http://www.boxerworld.com/forums/showthread.php?t=11396
Lastly, of course, here's a little information on health issues. Sadly, these are not rare problems in boxers, they are very common and becomming even more so. Screening of breeding stock for these genetically inheritable diseases is imperative if the health of the breed is not to deteriorate further, and really, the most important part of responsible breeding of these dogs:
www.boxerworld.com/health-testing