The two changes you can make right now are to displace the amount of water in your toilet tank and check for leaks. First, fill up a plastic juice or milk jug with pebbles or sand, screw the lid back on, and place it in the back of the tank clear of any flush mechanisms. A commercial toilet tank bank will also do the trick. Just make sure you have at least 3 gallons of water left in your toilet tank for proper flushing. Now, check for drips. If you aren't sure if your toilet is leaking, put a few drops of food coloring in the tank and see if it ends up in the bowl. Leaks can waste up to 20 gallons of water per day. It's worth springing for a plumber if you can't fix the leak yourself.
If you have the means to replace your toilet now, investigate low-flow and dual-flush options. A low-flow toilet uses 1.6 gallons per flush. A dual-flush toilet uses different amounts of water depending on what you're putting in the bowl—less than a gallon of water to process liquids, more to process solids. I was intrigued by the dual-flush settings and spent uncountable hours researching flush rates, flow rates and waste disposal. The company that got consistently high marks for efficiency and efficacy was Toto. I went with their dual-flush Aquia III and am a mighty happy (and water-efficient) gal. One note: There is less water in the bowl. Since stuff can stick to the sides of the toilet, I spend a little more time keeping my toilet clean than I used to with my old water-hogging toilet. Bu it really isn't a big deal. I contacted Toto and was told their low-flow toilets have a more powerful flush than the dual-flush varieties, so am going to try one of those out when I convert my downstairs closet into a half-bath.