To have a document, you need something you want to communicate. You need to write something appropriate for your audience--but first, you need to identify who that is.
You can break down identifying your audience into three main questions:
Who is using my resources?
Why are they using my resources?
What do I want my audience to know or do?
Consider some dominant traits of who might use your resource--who are they? What do they know already? Are you writing an informational flier about why people should vote for soon-to-be 18-year-olds considering voter registration, or is it for older Americans who have been registered for years and have not voted?
Consider some possible use cases for your document. If you wrote a document teaching basic information literacy, is it for people Googling information about how to determine if an article is true, or is it for people who came to your site seeking information literacy skills directly? How are they using my resources?
Will they be scanning the page looking for a specific word? Will they be trying to blitz through enough of the page to get the gist? (Spoiler alert: no, they probably will not be coming to read every word.)
You have something in mind that is the reason you are writing this content. What is it?
Federal Plain Language Guidelines. The Plain Language Action and Information Network (PLAIN), 2011.