Someone asked me recently about breaking into the video game industry as a writer / narrative designer. There's so, so much good advice out there that I only tend to hit this topic on rare occasion. But it's been a while, so let's go!
(Why my answer is worth anything: I've been doing this for about fifteen years and I've hired a lot of writers and editors. Why my answer isn't worth anything: My view of the industry is fairly narrow and I haven't tried to break in for a while, so I'm arguably out of date.)
First: Write, write well, and write video games. Published non-games material is great, but at this point there's no reason not to put together a Twine game or similar to add to your portfolio. Show you're interested in the medium.
If you're applying to a job that requires a writing test (most companies serious about narrative will require one), do what the test says. Follow instructions. Show you can deliver what your client is asking for. Do it well.
If you're submitting other samples, make them diverse in style / tone / character voice--show range. If you want to be artsy and experimental, you can INCLUDE that but it shouldn't be the focus. I want to know someone can tell a straightforward story adeptly. Basics first!