Online copy is the foundation of a website. It is constantly in view and is usually the focal point of a page. Good online copy can also make the difference between a site attracting regular traffic and becoming stagnant.
Your writing needs first and foremost to have the reader in mind. The copy should be strong, clear and easily readable (remember the principles of scannability, including bullet points, bolding, short paragraphs and headings), while still making maximum use of key phrases.