The Need to be Flexible as a GM
Writing can be a lot of fun. That's what the essence of Play by Post roleplaying is. It is writing. Don't let those that think less of roleplaying say otherwise. Writing a play by post roleplay is like writing a novel with other coauthors. Everyone is there to have fun.
So you find a story and you think you might want to join it. So you create a character and post it so that you can get into the game. That's a good thing. Now the fun should start.
And most of the time it does. Some times however you come into a game and the GM is a hardcase. Its his story and you'll do what he says or else because they have every minute detail already planned out ahead of time and everyone has to follow the plan to the letter. There's no way around it. You either play it his way or you can go find another game.
If that describes you as a GM, you really need to take a step back and look around. Your group is probably ready to string you up and leave you in the nearest tree.
Its not fun to have every one of your character's actions determined by the GM. The GM is to set the stage and then the other characters react to that.
So a major rule for the GM to keep in mind is to be FLEXIBLE. If one of the players posts the unexpected and suddenly you're straight line to the end goal is suddenly not so clear, don't panic. Adapt to it and move on. You can always redirect the story back to your agenda later. Let the players have freedom and fun and the game will continue because they are having fun.
So if you come into a game where the GM is inflexible and demands that you retract your post because you had the character turn left instead of right, then it might be time to find another game and let the GM have his story.