Hey Philippe
As far as I understand it ensuring the best results relies upon accommodating the IR.
Light - You obviously don't want to be capturing in the dark but you also don't want over exposure. When working with other Kinect capturing software like Faceshift I use diffuse lighting which also seems to work great for IpiSoft. You can find a great tutorial on creating diffuse lighting here.
http://www.youtube.com/watch?v=Z7PPWtmbtjkCreating a diffuse light helps to soften the harsh termination lines you may run into when trying to add light sources from say a point lamp or construction lights.
Environment - Reflective surfaces are a no go as they will bounce the IR and not give accurate data.
Clothing - Nothing baggy and nothing black as I believe it will absorb the IR rays. Relatively tight (not body hugging) attire is fine. Just remember its all about silhouette, if you give off an inaccurate silhouette chances are you will track inaccurate data.
I hope this helps
**Edit** just found this in which GreenLaw answers your exact question
viewtopic.php?f=2&t=6303