The first thing to remember when introducing two rabbits is that they need to be neutered before you start trying to put them together. After this initial step, all you need to do is give the rabbits an opportunity to become familiar with each other's scent. A large open space - like a very large dog- or bunny-proofed room - works best here for both animals' safety and because it allows them to explore at their own pace until they are more comfortable around each other. Remember that rabbits have different personalities just as dogs and cats do, so some may take longer than others to adjust fully. Keep an eye on any scuffles that might break out between the two of them but if everything seems peaceful then you can let them stay together overnight.