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I use a buffing technique with the heel of the blade when I shave under the chin. The heel of the blade doesn't get as much use as the rest of the blade so it tends to be a bit sharper too.
Disclaimer:
I know some people use the heel just as much as the rest of the blade. From the blades sent to me, I have noticed that most people don't use the first inch of the blade as much as the rest. YMMV.
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+1 to techniques already mentioned. Also, take a look at Chimensch's 30th shaving anniversary video--he holds the blade in both hands as he goes ATG up the chin and upper lip. After seeing his video, I added that technique to my shaves and have had very good results. Using both hands really helps with keeping the angle very flat there, and you can also feel what's going on better.