Because the bulk of a normal post will be written text, essential points to consider include:
Language
What is the language spoken by most of your readers, as revealed in the market research above? Do they speak English, French, or vernacular, etc.?
If English, do they speak British English, American English, or localized dialects like Australian English?
Correct spelling and using the proper dictionary will distinguish the writing on your site from mediocre sites.
Voice and Tone
There are several things to consider when talking about voice and tone, and these are but two:
Some brands prefer being formal when considering the vocabulary to use in their blogging, while others choose to be informal.
For instance, a financial magazine like The Economist uses formal language, while hip hop magazine, The Source, incorporates slang in its writing.
A few brands make the most of both worlds by incorporating slang and urban words in their blogs. They may even use colorful swear words and crude verbiage in their writing as stylistic devices to create shock and awe.
Anyway, when considering the terminology to use in your writing, please be mindful and use correct grammar and simple vocabulary to ensure high readability and comprehension.
Consulting a dictionary after every other sentence is no fun at all. Make your posts scannable and a pleasure to read.