You'll know all this already, I'm sure, from reading threads on here!
1. All bunnies must be neutered/spayed with time for hormone levels to settle before introductions are made.
2. Small, neutral territory for introductions (the pen I use is 1m square).
3. Scatter food over the floor and add huge heap of hay - eating is a social activity
4. Allow yourself at least 3 days to be with the bunnies constantly, including overnight as needed. Once they are together, provided there is no serious fighting, do not separate otherwise you're starting from scratch again
5. Chasing, fur pulling, humping is all to be expected. They need to sort out their hierarchy! Don't get involved or touch bunnies unless you really have to - only intervene if they are locking onto one another and swirling round on the floor, digging at one another's stomachs. An oven glove might help to protect your hand!
6. Be patient! Bonding a trio is going to take longer than a pair cos there are more combinations to consider and a greater hierarchy to be decided.
I'm sure other people will add to this! x