Once you have a map of your presentation, you can begin work on specific content. The essential form of communication on the web is still text. Even if you're using multimedia with pictures and sound, you're likely to also be using text. Indeed, most of the time you will want to get your ideas across with words. So your words need to carry meaning.
Good writing is clear writing.
Don't worry about long words or complicated sentences, worry about clarity. One way to ensure that your writing will be clear to your readers is to have others review it, preferably more than one. Let them make notes and give you feedback. Critiques are often hard to take, but the best way to make sure that your text is working is to find reviewers who will be honest with you. Another technique is to read aloud what you've written.