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)
This should follow what is in your print and promotional material
Make sure everyone who is contributing to the site is aware of these.