Like Gsulfrage said, I think the biggest key (especially on board bows) wood selection is most critical. I also have been lucky to have only broken one so far, and I made it knowing ti would probably break because it was a questionable board.
When I selected the 2 oak boards I have used so far, I had to go through every single stick of wood in 2 different Lowe's stores. and now they have no good boards left because they don't go through a lot of stock and I took all the good ones, lol.
I think the biggest help to me in learning good wood selection was this page:
Now the rest of the build-a-long may or may not be frowned upon here because he leads young bowyers astray with fiberglass backing, but his tips on wood selection really helped me.
http://poorfolkbows.com/oak.htmOthers on here may be able to recommend other resources on proper wood selection, but I'm a visual kind of person and seeing pictures of "good" and "bad" helped me know what to look for.