http://learn.adafruit.com/how-to-build-a-hardware-startup
I don't know if you want to do a startup, but there is good information in the guide.
Here are some other blog links that might be good starting points for further reading:
http://octopart.com/blog/archives/2013/10/electronic-compone...
http://octopart.com/blog/archives/2013/11/what-every-hardwar...
http://pinocc.io/blog/open-source-hardware-business/testing-...
By the way, Octopart and Adafruit are really great.