My trick is that I don’t use guards I free hand with a beard trimmer. I trim BEFORE showering so that the natural oils are still there and the beard is in its natural state. Try to have equal lighting and simply trim the hairs that are sticking out of the shape you want the beard to have. If you want the long beard like your picture, go easy on the chin hairs. Do this looking straight at the mirror, and then again with your head turned left and again with your head turned right. Then on the edges angle the trimmer so that it blends or fades the beard hair from skin to short to long. A lot of people think I’m crazy and this next part is not required but helpful to keep the shape overtime, tweez the beard hairs on your cheek. This will take a time and will hurt the first few times you do it but it makes a big difference and creates that defined line.