Living wills and advance directives are a good starting point but they may not be enough. If one is potentially near end-of-life and is serious about DNR-type wishes, it behooves one to get something like a DNR bracelet and/or a POLST document posted on your fridge, so there are no misunderstandings with first responders. There have been a couple NYT articles about this recently. As others have echoed, get the information specific to your state.
http://opinionator.blogs.nytimes.com/2015/04/29/the-right-pa...
http://www.nytimes.com/2015/03/17/health/the-trouble-with-ad...