If you have decided to start writing a book, articles, essays, I have a few tips for you. Now, I am not an expert but I do have some experience and I love to help people if I can.
1.) Be open to writing about different topics. I have written How To articles about plants, inspirational articles, educational articles, (am writing) suspense/action novels, write-ups covering events. It is always a good idea to branch out.
2.) Research different writing styles. Third person, first person, creative writing, find out which writing style you work best with. However, do not feel like you have to stick with one writing style. Try them all.
3.) Always assume you could get better. Don't ever think that you everything there is to know about writing. Do research. Study textbooks. Read other people's writings. There are always places you can improve, whether it be your grammar, punctuation or writing style. Also, ask for other's people advice/experience. Do not be afraid to hear other people's criticism.
4.) Read what you write aloud. When you are finished writing your article, chapter or essay, read it aloud to yourself (or to others). You will be able to pick up on some mistakes you may have missed.