Personally I got into games writing through being a game designer, and I got into being a game designer through being a pixel artist. Get into the industry via any means you can and then just let everyone know that you do writing so that when they find themselves needing someone for a spot of writing, they know who to throw a bone to (that's basically what happened with me, because as a salaried employee you'll be a crap-ton cheaper than hiring an external writer).
Oh, and as Monstro said, be multi-skilled. A writer who doesn't know about game design is no use at all.
What he said. I find with most positions within the indiedev industry, you have to know how to do more than one thing. Since budgets are small, the people that tend to get hired are the ones who can wear a lot of hats.