Source: Creative Commons image on Flickr by betsyjean79
First things first: You need a bathroom fan. Moisture is the enemy of houses, and bathrooms produce a lot of it. While you are getting a bathroom fan, you should step up and buy a two speed one that can be used at low RPM full time and high RPM when you are showering. The need for the two speeds will become more important as you improve the rest of your house and it's good to get it out of the way now.
Bathrooms use a lot of water. If you were building new I would tell you to save some of that water by plumbing for gray water reuse from your shower and sink, but it can certainly be a difficult even for new construction just to make it legal, on old construction you also have to get under the floorboards and replace old pipes as well as installing new ones. This is not for the faint of heart.
But you can still reduce your total water use by installing recent low flow toilets and shower heads. Low flow toilets have improved a lot in the past fifteen years, and now they work just as good or better than the old water hog ones. I don't know about low flow shower heads. I don't get a chance to try many and you only really notice if it's low flow if you don't like it. I wish that there were somewhere You could test them all out, like the Home Depot. I would like to try some of these shower heads from Bricor out, when I move I think I will get one but I have no idea which one.