Just some stuff I have picked up which I think is handy. With the hair and neck thing, these are personal style choices I have made. They're not ART RULES that must be followed absolutely. They're just things I do.
I'm so happy I came across your tutorials on tumblr! *u* Probably gonna print them out and decorate my walls with them!
And yeah, the thing about necks needs to be emphasized MUCH MORE for amateur artists. As with everything, there is no fixed rule, but people with little experience tend to go for the "lollipop stick" school of neck-to-head ratio, which may be really annoying in an otherwise good design. Especially when the character is supposed to be fully grown-up and/or masculine and/or stout. Personally I'm way more forgiving of transparent anime hair than too thin necks in character designs, because in case the latter occurs it's much more obvious when it's not a conscious choice but blatant lack of understanding on artist's part.
Haha yeah, well, I guess we've all be guilty of the skinny neck at one point or another. I know I have! I think necks can be hard to get a grip on because people tend to want to master the appealing aspects of a character's face and forget the neck. Which is ok, as everyone learns stuff at a different rate and people usually get it eventually.
Yes, definitely everyone's guilty of it at one point.
As I thought of this neck problem more, I realized it bugs me so much because it also touches related fields of art, like costume design and photo manipulation. Turning a small person into a bigger one via fat suit or Photoshop magic doesn't quite work if the model's neck is left skinny as always. Sorry, just a random observation.