Notes on my Snake Plant

I've had my snake plant for about eight months now and I'm still not totally sure if I'm watering it right—I've been doing it maybe once every three weeks, but the soil never seems to dry out completely. Should I wait longer between waterings? I'm also noticing the newer leaves are slightly narrower than the older ones, which makes me wonder if it's not getting enough light where I have it by the window. Has anyone else dealt with this?