The best tips for writing are:
Read a variety of different styles and genres, fact and fiction, news and comment, blog and print. Get a feel for what works well in writing, what writing style suits you, what writing style will suit your audience.
Study rules of grammar, punctuation and typography. If you don't get those right, it doesn't matter how good your content is, you'll really struggle to get any credibility as an author. Even down to little things like the difference between hyphens, en-dashes and em-dashes – they might sound like pedantic hypercorrectness to you, but they all contribute to the impression of quality that your readers will form.
Learn about your subject matter. Write about something you know about and are interested in. Research around it. If it's a topic area that has been covered extensively elsewhere, try to find a new angle so that you're adding something of value and not just rehashing the same stuff that's already out there.