After a year of trying to get into nutritional ketosis and failing, I luckily ran across this video, I explains things in such a clear manner, that I was easily able to get into ketosis and begin reaping all of the health benefits. I later read Mercola's "Fat for Fuel" and that really filled in all of the gaps in my knowledge base.
If you want to learn what ketosis is and how to get into it, without messing around, this is the information that you are looking for.