There are two important things - don't let dust build up as it scratches, and don't use too much water. The instructions with ours suggested using a static cleaner - you know, like those swiffers? - to clean once every day or two. Then when you mop, don't use too much water, and just half a cup of white vinegar in a bucket of water is fine. If you want to, you can buy floor cleaners that are fine for floorboards, but the vinegar seems to work as well as is probably cheaper.

My MIL uses her steam mop on our floors every now and then and they come up well from that too.