Be as self-contained as possible. Be especially careful with expectations of supplies, equipment, personnel at your venue. Confirm everything in advance. The extent to which you can expect your needs to be met at the venue depends on many factors, such as whether it (and/or the organisers) are used to hosting conferences, the amount of spare money available for contingency items, the formality of the conference, and its remoteness (in the world, language, culture, and in relation to "usual" services, eg telephone) (see Crashes and Backup / I11).
Allow time to get the system working smoothly. This includes training of staff or volunteers (see Roles / P2; Volunteers / P5). Test procedures beforehand. If the conference's first experience of participative messaging is disconcerting, enthusiasm will rapidly fall away.
Keep as simple and human as possible, whilst incorporating adaptability and robustness. Try to build a safety-net dimension into the organisation - whilst all the pieces may function very well, it is sound to provide a backup system if they do not. This also applies to people who feel that the structures imposed on them (with the best of intentions) are alienating and prevent them from getting their message across and interacting with like-minded participants.
And remember in the best of worlds, systems continue to fail. It is important to be aware of possibilities known to all who have set tested interactive conferencing to date. These include: vital hardware crashes, connections that don't work, vital personnel who are sick, fuses, incompatibility where everyone swore there was "no problem", etc.