What are your guidelines on cheek line height and neckline height?
Cheek line height:
Imagine a horizontal line going across your face at the bottom of your nose. That would be your maximum cheek height. Shape the line however you like below that point, depending on your face, desired look, where your mustache falls, etc.. This is another case when the electric shaver/trimmer is 10,000,000 times easier and more accurate than a razor.
Neck line height:
There are so many different opinions on this. Here’s what I’m feeling today: If you’re going with a shorter beard, keep it above your Adam’s apple. That’s usually where you have a face/neck breakpoint, and that’s where your beard should stop. Everyone’s got a different neck, though, so experiment. If you’re a heavier set hombre and the face/neck breakpoint is a little blurred (not necessarily a bad thing, and growing a beard is the best thing you can do to hide it), you’ll want to put that line lower on the neck to add length to your neck.
For longer beards, don’t worry about it.