1. Initial sketch. Done in Photoshop with my favorite faux pencil brush.
2. Inking, inking, inking. I use Clip Studio Paint for my inking. It has a line stabilizer, so you have cleaner lines. It's also fairly compatible with Photoshop, so you get transparency behind lines.
3. After I ink, I take things back into Photoshop and use the warp tool to push and pull areas that feel too squished.
4. Colors and texture. Pretty simple. Background texture, then a hard edged brush and the selection tool to divide up areas. Each color on a separate layer, another texture overtop to create the worn look. Honestly, it's not hard... but I could afford to do an entire tutorial on speedy flat coloring.
Keep everything on separate layers. It may make for a big file, but it's worth it in the end to be able to endlessly edit.