Hi, Zafnlfl! Welcome to BB!
I would recommend reading up on the "litterbox training" section of the site for some great ideas - you can find it here: http://www.binkybunny.com/BUNNYINFO...fault.aspx
A couple quick things - what type of litter are you using, and did you put hay in the box on top of it? The reason I ask is because buns like to eat and "go" at the same time. Also, if your bun is already using one area of the cage for his potty - put the litter box there.
Depends on the size of the bun, but here is what I do: I got one of those "sifter" cat litter boxes - the one where there are two trays - one on the bottom where I put the wood pellets I use for litter, and then the other tray (the screen one) goes on top of that, and I put a couple handfuls of hay on top of the screen, spread it out.
I also have a hay rack that I made that hangs on the crate above the litter box - so my bun can either eat the hay at his feet or from the hay rack.
The urine goes through the screen and into the pellet litter. The poop pellets stay on top with the hay. It's easy to dump the screen tray every day, and put in fresh hay. When you do that, it's easy to scoop out the pee-soaked areas in the litter and put some more fresh in and mix it around, but the screen back on, and voila, clean litter box!
I do this every day and keeps everything fresh!