English is not everyone's first language, and everyone who can read English will differ in their literacy and cognitive ability. When writing for the web, users should write at an eighth-grade level, which means you should:

• Use short, simple and declarative sentences. 
• Use images to enhance understanding of what is being described in your text. Images also break up large passages of text, which improves reading comprehension.
• Write in short paragraphs (3-4 lines), to increase the amount of white space on your page. Short paragraphs and white space are known to improve reading comprehension. 
• Break up long passages of text with white space by using bulleted or numbered lists where possible.
• Break up long passages of text by using headers to divide content into clear subsections. 
• When possible, have a colleague read your content before it is published, to check for clarity and grammatical errors that spellcheck wouldn't catch.
• Always use spellcheck to ensure you have no typos. 

Additional benefits of simple language and white space

People do not read as attentively online as they do in print. In fact, web users are generally only scanning a page to seek out the relevant information they're after. Web pages with short sentences, short paragraphs and headers helps a user quickly and easily find the information they need.