Different channels require different styles of writing. A quick post on Yammer or an update on a blog will need to be written very differently to a formal letter informing staff of a significant change that has an impact on them.
There are many style guides out there and you need to understand what works for your organisation and audiences. In developing a style guide you should be mindful of how language is developing and the Government Digital Service style guide along with Plain English principles are often a good starting point.
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The principles to consider before developing digital content are similar to those for any other content, namely:
Generally speaking, the following content works well for digital: