Easing up on the steering is how you correct an understeering car. If you can shift a little bit of weight to the front that will help too, but usually doesn't seem to be enough by itself in my experience, and generally means slowing down a bit. Often after you get control back, particularly if your weight is better balanced, you can turn the wheels just as far as they were when they were sliding without losing grip. It's just really counter-intuitive to steer less when the car won't turn, you want to turn more, MORE!
Ideally I like a car that will oversteer a tiny bit into the corners, and understeer a tiny bit coming out. I can't stand a car that won't get into the corner, and if the tail comes out after the apex you're bound to lose gobs of time.