I can only agree on that what Kat said. Additionally I'd say that, as stupid and banal it may sound, first of all you have to practice writing. And there it doesn't really matter (especially if you're a beginner) if you make mistakes or not. You just need someone with a high level of your target language (so German) like natives or advanced learners. Then you need to decide how you want to practice. like Kat said, you can write notebook entries here (so more or less longer texts like stories, experiences etc.) or you can chat with someone who's able to speak German and try to practice while chatting.

As always, learning a language is pretty much up to what you enjoy doing. You don't enjoy it, you won't learn very much, so you should pick something you really like. To improve your writing, you could of course just pick a German penpal and ask him to correct your writing. Or use the italki-family and make one or even more entries every day. Another thing that works well would be to get yourself an audio book and the book itself as well, listen to the text, write it down and compare it with the original. It's very practical, because you train your listening skills and your writing at the same time. Of course you can do both for the maximum effect, but don't forget to enjoy! :)