I stated with a rough pencil sketch then inked it with a brush pen and colored it with watercolor and gouache on a watercolor postcard. Reference I used was this excellent photo - https://www.pexels.com/photo/tree-wild-squirrel-monkey-97827/ photo by Mike from Pexels.com
A working page for a book i am developing about vampires. i starts with a raw ink sketch, gets scanned and i work them up on a xp pen tablet - but this is just experimental - and not final.
Illustration painted with watercolors and outlined with pink pen. The borders were achieved with washi tape (low tack and unlikely to tear up your paper.)