Tone of voice
I've worked for several brands developing tone of voice. Before you start a lot of questions have to be asked:
Where you want your brand to be in the mind of your target audience.
A promise of its benefits to your customers.
What you do now.
A desired and possible future.
What you stand for.
What it’s like to work for and with you.
Who are you talking to and what's the best way to communicate.