Well, it’s such an individual thing. Some rabbits just don’t want to be with other rabbits. So people have to be prepared that they may end up with two rabbits that can never be together. Some people do play dates at the shelter to see if the rabbits get along. I don’t know how this can possibly be a good indicator in such a strange place, but people have found success.
Only get another rabbit it YOU want one. Seriously.
They don’t have to be the same size or breed or anything like that. Just get one that’s neutered. Maybe an unspayed female would be OK, but I think they’d be calmer/less territorial if they’re already neutered.

There is nothing sweeter than two bunnies in love. There is also nothing worse than two bunnies fighting. Megabunny is right, only get another bunny if YOU want another and be completely prepared to have two single buns if you end up with two that just can’t get along or if you don’t have the time/patience/etc to work through the bonding process. I believe that all bunnies can be bonded given enough time and effort — many people give up on difficult bonds (its looking like adding my single bun to my pair may be one of those cases due largely to time).

I agree with the others – only get another rabbit if YOU want another bun!

Bonding can be extremely difficult. I am a firm believer that any rabbits will eventually bond but it can be a very long and difficult and stressful road! A LOT of people give up so it’s important that you are prepared to have two separate rabbits in the chance that it becomes too much for you to continue bonding.

I would advise taking your bunny dating. It’s a GREAT way to judge your rabbits initial reaction to the other rabbit. They are not as territorial because they have not claimed the place and both buns are slightly nervous so it help with any general aggressive feelings/tendencies to battle it out immediately. You are looking for a POSSIBLE easier bond when you take your rabbit dating, it is definitely not a guarantee! I also advise “dating” because it’s typically done through a shelter. No rabbits should be together unless BOTH have been altered. When not altered they are way more territorial and a lot more aggressive/defensive of their things making serious injury between the two a pretty risky situation. I have known multiple people who failed to follow this advise and ended up regretting it when another rabbit was injured. This can happen with bonded buns as well but is way more common and risky with unaltered.