Create something! This can be either writing somehting more traditional, or a more interactive web 2.0ish thing (I know a lot abaut these, and there are many different ways, so if you're at all interested please ask), or if you're less into writing serial art/comics and animation storyboarding also offers the storylike elements you want.

Don't fuzz about quality or dignity. Start writing crap quality self insert fanfictions that are just an instant reward guilty pleasure at first.

Try to put yourself in the mindset that you ARE playing a computergame and that it just happens to run on the wetware of your brain instead of the computer. Set up rules for yourself and act within them and stuff like that.