Let me start right away by saying that this is not a thread for sharing links to writing guides and the like, since Ashenmoon already did a great job of that in this thread.
Instead, I'd like this to be a place where we can share our own private tips and quirks we use when writing. I figure that we can pick a form of writing from time to time, and we'll share what we know and have discovered about it with each other.
As the most familiar form of writing to me, and probably many others, I'd like the first topic to be Forum Role Playing Games.
Here are some questions to help foster discussion: What are some tricks you employ when writing for a forum RP? How do you make yourself update regularly? How do you force yourself to update even when your character is in a situation you don't find interesting to write? What special tools do you use? Any other tricks?
If you've got another thought provoking question, feel free to add! Now let's get this thread started.
Separating my own answers from the main post to avoid confusion.
In recent times, when I begin to write for a forum RP, I create a folder on google docs and start each update as a document named "dd/mm/yy Update:#". Then I just write my post in there and paste it into the forum thread when I'm done. This format helps me keep track of old posts when I need to look things up and google docs lets me write even when I'm not on my own computer and live without fear of my writing document crashing without saving. Writing a post directly into the forum box is a great risk (unless it's a short single-paragraph update like my posts in the Utmost Land) and the minor inconvenience of having to redo all your formatting when you paste your post is easily outweighed by all the benefits.
Now, besides the google doc, I have a plethora of other tabs in my browser that help me. First of all I keep tabs of my last update and the latest GM update, letting me quickly check things and keep consistency. Besides that I also have a thesaurus, a reverse dictionary, tip of my tongue, and a rhyme finder at the ready for when I need to find that one word. Also, English being my second language I sometimes find myself not knowing what a word means, sometimes I even doubt if a word I thought I knew really means what I think it means. So I find that sometimes just looking up a word in a dictionary (either an English or a Language-to-English one) helps a lot to keep my flow going.
Sometimes, if I feel unsure about my update, I ask Tim to take a look at it before posting. He can quickly spot if I failed to address something or wrote something unintelligible. Most of the time he'll just say "Looks great, post it." Which is a nice boost of confidence anyway.
Now, as for motivating myself to write, I'm usually pretty damn terrible at keeping a schedule. Something I've found though is that I easily get stuck in a very negative spiral if I ever miss a deadline. When I miss a deadline, I vow to myself that I need to make an update that is twice as good to make up for it. Don't ever think like this. It's only going to make it worse. When you suddenly put a higher expectation on yourself like that, updating feels more like a chore than fun, and you just end up avoiding to think about it out of shame as the time goes on. It's important to get out of this poisonous mindset as fast as possible, dropping the expectations and just writing an update. It doesn't matter if it's just 3 lines long and not at all proportional to the 4 weeks it took you to finally post it. The game goes on and you'll soon find yourself a lot more inspired to write the next time it's your turn to update.
Forum games is all about quantity and not quality, and I don't mean walls of text, I mean post count. It's better to be the most frequent updater with short posts than the least frequent with the biggest. You'll find your character's story to progress a lot faster and you'll get to spend more time thinking about what to do next than just sitting at the desk slamming the words down. Quality will come over time and there's no use obsessing about it.
As a last piece of advice. Whenever I've read something that turns me off the game, like my character's plan getting ruined or a lame side plot requiring my character's full attention, I've found that just going out on a walk (with the dogs in my case) calms me down and gets my inspiration flowing. Whatever problem seemed insurmountable or just plain boring turns into a writing opportunity quite quickly.
Edit: Extra last advice. I always reread my post after posting it and find quite a few things that I missed, like spelling or broken formatting (or in this case, a wrong link). 9 times out of 10 my post will be edited within a minute of my posting, sometimes twice.