One of the techniques that I am using and finding good results when going ATG is one (I mentioned this before, but I'm just reposting as part of the list) a guillotine stroke. This one seemed to do the best. Two, a scythe stroke not as good as guillotine but safer. And lastly using a buffing motion has worked with good results in the most troublesome spots.

I have notice that I have to pay more attention to detail on my angle of attack and pressure when doing my head than on my face. Not just for the fact risking a cut but I find that I dull my blades the most when I tend to use the wrong angle and pressure on my head. Probably because while on our faces we have fat and other soft tissues to cushion the blade but with the head we have hard bone pressing on the edge dulling it if we are not careful.

When I do the back (the back only) of my head I don't use a mirror. The awkward angles and images to just see back there is more of a problem than a help. I normally go by feel. I feel the back to see if I am missing any spots and imagine just combing what I use to have, or at least that is the feeling. But I have notice with a few of my first attempts that going without a mirror for the back of my head it is actually easier than what most people make it out to be and as your confidence gets better so will your results.

Good shaving