I marvel at the language skills of those who live outside of native English-speaking countries. Several friends speak two or more languages. I find that phenomenal. Although I have studied French and Spanish, I am far from conversant in either language. English is my one and only and sometimes I've wondered about that..
Citing your sources helps you earn credibility. Whether you write non-fiction for online visitors or offline readers, proper citing of sources is critical.
It may come as no surprise to those who read online that narrow text columns are preferable to wide ones. Good web developers pay attention to browser resolutions and screen sizes to ensure that their web pages are the right width. The length (i.e. word count) of an article is the writer's concern.
Write because you love writing. If your goal in writing is monetary success, you may be disappointed.
Throughout history, writing hasn't been a 'get rich quick' scheme for most writers. In fact, many famous writers, such as Edgar Allan Poe, died broke and broken. If you are writing for any other reason than you absolutely love writing, you are writing for the wrong reason.
What you say might be less important than how you say it.
This holds true, in fact, even truer for material that is published on the web.