Okay often when I write I know where I want to go with the story but often the trouble I have getting from point A to point B and even when I have a few of the characters picked out I have a hard time figuring out how they fit into the story and when it's best to introduce them. Anyone else struggle with this problem?
If you're having trouble figuring out where your characters fit in and when you should introduce them, are you sure these characters are right for the story? Are they even meant to be in the story? Seems to me that if a character is essential to tell the story, then he/she would have a role, which solves the "where they fit in" question. If they have a role, they have a story, which means there's bound to be a beginning, which solves the "when should you introduce them" question. Sounds like you developed your characters separate from your plot/story?
When you create Character and Story together, as one, not one then the other, you do not have that problem. Stories are about characters making choices, based on their motivations (what they want) and then dealing with their consequences, ending in them winning or loosing, but either way changed forever. You have to make the story about want the character wants and how he/she goes about getting it.
I do have that problem. Interestingly, and as the two posts above say, the more that I think about my characters, the more the plot issues seem to resolve themselves. Like, I think about the the plot issues from their perspective and what they would do, and solutions seem to crop up. Sometimes it gets me to B, sometimes to C, but its always interesting, and I think makes for a better story...
To move the plot forward (from A to B) you develop scenes, and to develop a scene you put the character in a situation or situations and have the char react. In other words whatever the char do, say, and even the description of the char should contribute in moving the plot/story forward. As far as fitting in the char and when to introduced them is concern, I too agree that char and plot should go hand in hand to make a story. But sometimes you may have developed a char without knowing what to do about it, and you may also come up with some plot without any seeming connection between the char and the plot but you somehow want the char in the plot. Here too I would say put the character in some situation of your plot and see how the char reacts. If your story involves high end scientific research and the char you have is a highschool football player who barely pass high school, dont be afraid to put the two together. It might bring some unusual twist to the story. So, basically what I am saying is: make the char do something in a plot situation, only then you will find out when and where the char fits in.