In a Brand Style Guide, You should include:

• Brand Heart: This is essentially a summary of your brand's guiding ideals, which can affect everything from how you communicate with clients to how you create websites. It consists of the reason you are here; the kind of future you want to contribute; the design and the tenets that govern actions.
• Verbal identity: this is what you say about your business, how you explain your goods, how you interact with consumers, etc. Including Messaging (Tagline, Value Proposition, Messaging Pillars/Differentiators); Brand Essence (Voice, Tone, Personality)
• Visual Identity: this is about Logo, Colors, Typography, Additional elements (if needed), Photography, Illustration, Iconography, Data visualization