Writing for the web is different than writing for print. Part of the issue is how people read online. They surf, skim and click.
1. Write shorter. If you are going to write long, you must give people a reason to read.
2. Be specific and concrete.
3. Use active voice and strong verbs.
4. Omit needless words.
5. Attribute your sources with hyperlinks. Give credit to ideas, text, photos, etc.
6. Link. Link. Link. Double check them after you publish. Make sure they work.
7. Use sub-headings, lists, key words and boldface type.
8. Be specific with headlines. Be clear. Use key words. Avoid puns.
9. Learn to be your own editor. Write. Save. Wait 15 minutes. Come back. Read it again. Then publish. Then read it again.
10. Mistakes, errors, typos and misspellings undermine your credibility. Run spell and grammar check.
Resources on Writing for the Web
How People Read the Web
How To Write for the Web (Online Journalism Review)
Tips for Writing for Online Media (Mindy McAdams)