As I'm still very new to grading I like to grade by making it a whole production. I check it over first and get an idea in my head (that's usually close, but almost never spot on), mostly just to see how I'm doing in the quick grade area.
Then I sit down and count out defects. I sometimes even sit with a notebook and write them down just to be sure I'm not missing anything. Start with the front cover corners, then look for creases/folds/indents/spine stresses. After that I check the spine and staples, page quality, and that the centerfold is firmly in there. Then I check the back cover for the same. After I count em all I compare to the range allowed for that many defects and then decide on a grade (or two, I usually will do something like 6.5/7.0, etc...) based on how good the front looks in general. If it has nice eye appeal then I'll usually assign it a grade higher in the range of allowed defects, if not, a grade lower in that range.
I'm hoping to do this enough that it becomes more second nature and doesn't have to be such a production anymore. But, that could be a while. Luckily, I enjoy doing it.