I found that the osdev.org was really a good place to start
with for all OS developers. It has a separate FAQ page which lists all
the common errors made and gives lots of other information like the
tools that we must be familiar with, the depth of knowledge that we
must have in the basic concepts of OS etc.
The link for the FAQ page is http://www.osdev.org/osfaq2/
I would also suggest that all of us become members of the forum of that
site where lots os questions related to OS design and development are
posted, and most of them would be relavant to us.