How to start a Story

I have had this plot for a web comic rattling around in my brain for some time now, but I keep having trouble when it actually comes to sitting down and writing it. Are there any suggestions on how to start my story? Also, if this belongs on another thread, just point me in the right direction.

A bit hard to suggest how to start a story when we don't have the slightest inkling as to what it's about.

Well, I assume you have some idea where you want to start. I recommend writing down the characters, settings, etc. you've thought out on sticky notes or something and then moving them around. Mad Libs is great for this, especially if you've got an idea of where your characterization will head.

Think about the inciting incident. What event lights the fuse for the overall plot of the story?

Personally I would recommend writing it. If you don't feel ready to do that, then think about it some more. Imagine how it starts, and figure out what you need to make it start that way.

At the beginning is popular, but in the middle pops up fairly often.

Best bet is to start with something that introduces your main character. Put them in a situation that's fairly normal for them, and which introduces their basic personality. Something Positive began with the main character sending an ex-girlfriend a coat hanger as a baby shower gift, establishing him as a sarcastic asshole who's not afraid to cross the line. Queen of Wands started with the main character waking her roommates up early in the morning to eat pancakes in their bed, establishing her as kinda wacky and mischievous. Penny Arcade started with a video game joke, establishing it as a comic with a lot of video game jokes.

So just start with something that establishes your characters. It doesn't need to be related to the rest of the story.

Sit down and write it until it gets out of your system. The longer you spend just letting it stew, the harder it's going to be to get it on paper. Don't be an ideas man. Write.