It is best to decide up front the tone of the site so it remains consistent – this can differ in different sections, for example a blog post or story feature can be more conversational and from the first person.
For consistency, decide on preferred formats, terms and conventions for commonly used content e.g:– Dates (e.g. 25th Nov 2017 or 25/11/17) – Times (12 or 24 hr clock) – Period dates (e.g. 19th Century or 1800s) – Measurements & units – Pricing / costs (£1 or 1GBP) – Wars (WW1 or First World War) – Use of Sentence case or Title Case when capitalising letters
This should follow what is in your print and promotional material
Make sure everyone who is contributing to the site is aware of these.