The best way to learn about style guides is to copy what others are doing and make it your own.
Quiqup Branding Re-imagined for the Future ~ Jake Wetton Freelance Graphic and Website Designer in Leamington and Coventry
плакат гайд Guidelines / Nikolaj Kledzik – Art Direction & Graphic Design – Bagel Street Café – Visual Identity // I like this page layout of how the "Bagel Street Café" has displayed its ideas for typography.
Bourne // consider making an identity guideline - poster, brochure?
Nooka Design Guidelines in Identity + Collateral
Made by Big – Strategic Design & Branding Practice: specialising in Brand Identity, Graphic Design and Art Direction.