1. If possible, consult with the DJ beforehand -- preferably to be able to match rough tracks to dances, but at the very least to get an idea of the presence (or absence) of traditional phrasing, tempo, etc.
2. Be aware that traditional phrasing may or may not be present; this puts more onus onto the caller to guide the dancers if needed. The caller has to be sure to pay close attention to the music, especially if it's not familiar.
3. Pick simpler dances: they tend to work better than ones with really complex moves in techno contra.
4. Find out if there will be black lights, strobe lights, or other lighting effects. These may affect how well you can "track" dancers from your vantage point. You will probably need to keep more of an eye on the dancers than you might at a traditional contra to keep the room together.
5. As a corollary to #4, be especially aware of crowding and other issues that may come up and pick dances accordingly; doing a dance with down-the-halls in a really crowded room gets really problematic at the bottom of the hall and you might not be able to see it as well as you would in a well-lit venue for traditional contra.
See something I missed? Sound off!
(This list will eventually be made into a PDF and made available for download on the Resources page. However, I wanted to open it up to comment first.)