Keywords are vital both for search engine optimization (SEO) and providing descriptive content for your visitors. Using keywords effectively in your content can make your text flow, improving its readability and assisting your visitors to fully understand what you are trying to say. But you will want to make sure that you do not overdo it by adding the same keywords over and over again. This isn't good for search engines nor will your visitors find it appealing. Read over your content. Ask a friend to read it too. Invite, and listen to, their comments. Fix what isn't working and check it again.
Good spelling is important. There are online spell-checkers and most browsers now clearly indicate your spelling errors when you are posting your content. Your web design software may have a spell-check feature too. Use at least one of these. When in doubt check with an online dictionary.
Google offers a helpful keyword tool that will provide good ideas for descriptive keywords you can use in your content. You can find it HERE.
The tone and language of your content should be uncomplicated, easy to read, make sense, and be easily understood. The easier your website content can be understood the more comfortable your visitors will be. That comfort translates into what is known as "dwell time" -- the length of time they stay at your website. Studies show conclusively that longer dwell times translate into greater sales. Keeping your content basic, uncomplicate, and without complex, technical, language will make for happier, and more, customers!
Use shorter sentences. Divide your content into shorter paragraphs. Separate the paragraphs by a single blank line. Use left or full justified text. Use headings and sub-headings where appropriate. Dark text on a light background is always easier to read. A very light grey (#efefef) background will be easier on the eyes than bright white. Standard fonts like times new roman or arial are easier to read than fancy cursive fonts. Use underlining, highlighting and linking, but in moderation. Text that is multi-colored, a variety of sizes, all caps or with excessive underlining and bolding is annoying, harder to read, and disruptive of the information flow. Emphasis is good but too much emphasis means nothing is really emphasized.
The primary purpose of your content is to impart information to your website visitors and, on an e-commerce site, to lead the prospective customer to the buying decision. There should be nothing that doesn't serve this purpose. Well-constructed content that delivers the message will also serve you well in regards search engine optimization. If your content is truly right for your prospects then it will be right for the search engines.