Here is how I decorated my moleskine sketchbook covers, extra large, they are of a size in between that of A4 and A5 and I got them in packs of 3. It’s of a very convenient size to make small sketches and jot down ideas. I don’t like books smaller than these where I can’t fit my hand on the page though I do use the A5 ones also for things like keeping patterns and such. I did the covers with Faber Castell metallic pens. Here I have different books for head drawing, figure drawing, perspective and also 3 books categorized according to brush tip, brush pen , flat brush and fine nib just so I can test how far I can push the drawing with one nib alone.
Here some pages from my head drawing book, character designs of a princess:
and here some from my figure drawing book, of an archer on horseback and a wanderer with a lantern:
Watercolor Journal 