I learned many valuable tips by reading Roger Sanders' book "From Idea to Print: How to Write a Technical Book or Article and Get It Published". This book covers everything that you need to know & do in order to get an article or book published. Becoming a writer isn't nearly as difficult as you think, but it does take work.
My job is an acquisitions editor for technical articles and books, so I've been through this process a few times myself. Even so, Roger taught me much. I think the most unique chapter in the book is about the author - publisher contract. There is much to know in this area, but not much written about it. The book is worth purchasing for this chapter alone.
Here are a few tips I learned from Roger about planning, writing, and editing a book / article:
1. Schedule time to write. If you wait until you're "in the mood to write", you'll never get anything done! Set goals for how much you want to accomplish and move to another section if one is causing you grief. Reward yourself as targets are reached.
2. Have a strong outline before you start to write. I know it sounds cliché, but the more up front planning you do, the easier the writing will be. Even for technical documents, you should "tell a story". Have a beginning, say a problem that needs to be solved; a middle, the search for a solution; and an end, a strong conclusion.
3. Let some personality show through in the writing. There are some cases where dry, factual writing is required, but where it's not, let the writing be conversational or slightly casual to be of interest to the reader. Always think of your reader. Even if the writing is just for a school paper, the last thing you want to do is to bore the reader so that the ending is never reached.
4. Diagrams and tables are useful, but ONLY if they are tied tightly with the text. Don't put them there just for filler because they'll never be looked at. The best idea is to add reference numbers to the diagrams and have text to lead the reader from one point to the next. If that sounds like too much work, maybe the diagram isn't really needed.
5. No one's writing is perfect... every author needs to review and revise their work many times. Most authors get quite tired of reading what they've written by the time it is "finished". Go through your draft many times, each time with a particular thing to fix such as typos or lists or passive tense.
6. For everyone, but especially if you are English-second language, consider reading the text out loud or have the computer read it to you. You may be able to hear problems in the wording easier than you can read them. Also, look at past comments you've received on writing assignments. Likely you often make the same errors every time you write, so pay close attention to how your previous errors were corrected, and go through your document to specifically focus on improving these problem areas. Learn from your mistakes!
7. If you're writing a technical document, your goal is not to make it "beautiful"... your goal is clarity. You want to ensure that anyone who reads what you've written understands your technical messages.
8. Get others to review your draft, but don't take feedback about your writing as an insult about you personally. If you do, you'll never be able to write. Not many people can write a first draft that is perfect... but with many revisions and attention to feedback you can get as close to perfection as possible.
9. Size matters. There are different ways to present your content. Is it an article (average 10 pages or fewer when printed), a tutorial (average 20 to 30 pages when printed), a white paper, a series of articles with a constant theme, or a book?
I read the book as it was being written and wrote a foreword for the book. I've worked with Roger on most of the 20 something books he's published and I'm glad that he wrote this book so I can have many authors to work with in the future who can hopefully come close to Roger's level of skill.