Awesome tutorial, paying special attention to the secret ingredients ie. the Micron .005 black liner is used for all the black lining, with limited use of the FaberCastell brush pens.
First of all, you cant get a decent result if you don’t have a goal. That goal for me was the image of a “Pre-Heresy Death Guard” from the Index Astartes article in White Dwarf.
The overall uniform color is a dirty white with obvious field wear, and medium to dark green trim. The look you are trying to achieve is a slightly roughed up feel, so drybrushing will be appropriate. However, you should layer on lots of very tight detail work on top of it, to make the final product still have a crisp clean look.
The goal is to make the rough white seem intentionally sloppy, not give the impression that you are a bad painter.