Entire books have been written about writing for the web. They have titles like, well, Writing for the Web. Also: Writing for the Web: A Practical Guide, Writing for Multimedia and the Web, and the nicely alliterative Killer Web Content. I imagine these books are used in Marketing courses, and I'm sure they contain many sensible words of wisdom. But honestly, it's hard to imagine anyone needing to study a whole book to learn a few basic principles.
For pretty much any home page, these principles can be summed up easily, as follows:
• Use concise, accessible language.
• Give the key information right up front. (Explain who, what, where, when, and/or how, as needed.)
• Get it right. (Don't allow any spelling or grammatical errors to get through your proofing process.)
• Make it easy on the eyes. (This is partially, but only partially, the web designer's responsibility.)
Here are a few examples of sites that get these things right and wrong.
Let's say I live in New York and I want to find an electrician. When I search for "electrician new york," among the top entries is Altman Electric. Altman's home page provides the essential information right up front: where they're located, what types of customers they service, and how to contact them. It meets the four requirements described above: no technical terms or excess verbiage, key information up front, no grammatical or spelling errors, easy to read.
Now take a look at another top search result, Apollo One. This home page fails on most counts. It doesn't look good. The text is too low on the page and full of errors. There's no mention of their coverage area except for the phrase "in New York" at the top, which is ambiguous, as "New York" could mean Manhattan, all of New York City, any of a number of conceptions of "Greater New York," or even New York State. For all I know, Apollo One could be a better deal for me than Altman, but I won't be finding that out, because if I need an electrician fast, you can bet I'd call Altman first.