Don’t worry about mechanics at the start. If you worry about the mechanics or technical aspects of writing from the onset, you will most likely get bogged down and lose your trend of thought. What are the mechanics you shouldn’t worry about at the start? Spelling, punctuation, usage, sentence structure, and typographical errors. These are things that you can always go back to after you’ve put all your ideas down on the page. Many famous writers owe their editors for the polish and cleanness of their works. I even have it on good word that some popular writers can’t spell very well! What is important is to get the ideas written. Your ideas are what make your work original and interesting. Remember first and foremost that you are a writer and not a proofreader or an editor.
Read. Everyday, whenever you have a bit of time, read. Not just anything, although that is good for a different reason, but the kind of writing that you want to do. If you want to be a journalist, read newspapers and magazines. If you want to be a novelist, read novels. If you want to be a poet, read poetry. Not just a little, but a lot. Get to know different styles of writing. Read works by great writers that you can model your writing after. Yes, I believe a lot of what you learn as a writer can happen by osmosis–in this case, just reading a lot of excellent writing–because you remember a bit of what you read (if your memory is better, you’ll remember a lot!), and what you remember will seep into your writing. But don’t just read excellent writing. Read the really bad writing too, and those in between. If you can distinguish the bad writing from the good writing, you’ll be able to apply that to your writing. You will know when your writing is good and when it is bad. You will learn how to avoid the bad writing and write better. I’m willing to bet that no good writer ever became good at writing without having reading a lot. What are you waiting for? Go get something to read!
Write about something you don’t know. Admit it. You don’t know everything. Nobody knows everything! There will always be something out there that’s new to you. If it’s totally new to you, it’s also probably totally new to a lot of other people. You could be filling up a niche. Who knows? It’s a great challenge to see how much you can write about something you don’t know. How do you go about it? Simple. Research.