The next six steps in Rob's guide:
5. Grab a 8.5 by 11 sheet of hex paper.These steps can be distilled into one instruction: make a cool map on a sheet of hex paper.
6. The scale should be so that it represents a 200 by 150 mile region
7. Draw in mountains
8. Draw in rivers
9. Draw in hills using them to divide the region into distinct river valley
10. Draw in vegetation (swamps, forests, desert, etc)
Since I'm using Jared Blando's How to Draw Fantasy Art and RPG Maps, I followed along with his step-by-step instead, which covers most of what Rob suggests anyway.
For your hex map, you can draw freehand over the hexes, you can draw a symbol in each hex representing the terrain type, or you can colour code your hex map, using green for forests, blue for water, etc.
Here's a (printer-friendly) numbered blank hex map I made using mkhexgrid:
Rob suggests a region map of roughly 200 by 150 miles, but I had to scale back the number of hexes to make it legible and printer friendly for standard 8.5 x 11 paper. I tried to put as many hexes as I could without making them too small. To account for fewer hexes, I'll be using 6-mile hexes. There are a number of reasons people think the 6-mile hex is superior anyway. Using a 6-mile hex, my region map is now 180 miles x 126 miles.
While drawing in the coast, I roughly followed the contours within the grey box I selected as the campaign region previously. Just treat the "grey box" (i.e. your campaign region) as your full 8.5 x 11 hex page and draw to scale.
I decided to continue with a freehand poetic approach for my region map. You can see I just treated the edge of the hex page as the borders of the grey box:
After drawing in the coast and islands, I just had fun filling in the mountains, lakes, rivers, hills, and forests:
These drawings were done in pencil and scanned using an app on my phone, so there's some smudging and fading, but you get the idea. I overlayed my blank hex map onto my drawing using paint.net. I may have gotten a bit carried away with the details. It would be easier to see the hex numbers and add points of interest if I had made features a little more symbolic with less shading. The trade-off is I'm inspired when I look at the map. C'est la vie.
The scale of your map features doesn't matter too much; it's mostly about what terrain the party encounters where and knowing how many hexes-worth of travel it takes them to reach a destination. Whether you draw big detailed trees or simply colour a hex green, when the party enters that hex, you know they're in forest terrain. Use whatever method inspires you or is easiest.
Next we'll stock the map with settlements, lairs, and ruins in Part IV.