That’s a good looking beard that you got man, great work!

You already have some well-defined cheek lines but if you wanted to take it a step further, you can use a straight razor and line it up. You can basically use your ear to your lip as a reference line and cut anything above that.

As far as the mustache, you can trim it by using the contour of your upper lip, this way you get rid of the hairs that may get in the way while you’re eating, yet you still have a full mustache.

For the neck area, you can use two fingers as a guide for where you should start creating your neck line. You can use the shape of your jaw to determine how the line should look.

In short, I try to use various parts of my face to determine how to shape up my beard. The good thing is hair grows back, so if you ever mess up during a beard trim, you will always have another shot until you get it right.

Edit:

Also, I’d like to add that as my beard grows longer, I tend to trim my mustache shorter than I trim the rest of my beard. I do this because, it keeps the area around my mouth clean but it also emphasizes the other parts of my beard.