The best instructions on litter box training can be found at the House Rabbit Society. The older the rabbit the easier it is, too. At this link, they discuss what is the best, safest litter to use, and how to go about it :-) http://www.rabbit.org/faq/sections/litter.html

Most rabbits take to the litter box quickly and easily, but they will likely continue to leave poops on the floor sometimes for territorial reasons. If your rabbit isn't fixed, they'll do this even more often, and they may sometimes urinate outside the box as well. If you fix your rabbit at a young age, you have a much greater chance of avoiding finding urine on your floor, and thankfully rabbit poo doesn't stain or smell, so, in my opinion anyway, it's not really a big deal if I find poops on my floor now and then. If it is a big deal to you, a rabbit might not be a good idea. The resource Galeanda provided (House Rabbit Society) is excellent, and for more information you should go there, because there are differences you may encounter according to region and individuality. But this is what I did: My rabbit came to me in a small wire-bottomed cage, so he wasn't used to using a litter box. For a few weeks, I kept his cage in his room, but I left the door open, and I also had a litter box in the room. He started using the box right away, and within a few days he stopped using his cage. Eventually I removed the cage. Then I let him have more freedom in the apartment, with a litter box in each room. Once he was used to the apartment, I gradually reduced it to just one box in his room, and one box in the livingroom. Now we live in a much smaller apartment and he only has the one box in his room. So this was the process, but there are many things to take into consideration to make the litter box look appealing to the rabbit. - Having fresh handfuls of hay in the box, replaced and replenished often, is a very good idea because rabbits like to graze and poop at the same time. - Use a litter the rabbit likes. Carefresh is soft and absorbent and a very good choice, but there are other options. - Maximize the placement for the rabbit's comfort. Always keep in mind that a rabbit is a prey animal and is generally concerned with staying hidden form predators (even if there are none in your home). Rabbits like protection from above, so consider using a box with a lid or placing the box beneath a table. Rabbits also like at least two exits, so if you use a lid consider cutting a second entrance in the side. You might arrange some things around the box to partially hide it, such as a folding screen. - Keep the box clean.