In order to be institutionalized, deliberative democracy needs places were ordinary citizens debate together. Such places should offer the best possible conditions for debating. These conditions are not straightforward to gather. A lot of empirical work has recently been published on this topic. Mini-public deliberations and deliberative polls are at the interface between academic research and public spiritedness stimulation. Our research team in Geneva organized four corpus of debate experiments. This paper investigates ways to optimize the experimental conditions in order to achieve two goals: collecting good quality data and opening constructive deliberative spaces. The first part of the paper exposes different mini-public deliberation experiments that were organized and gave rise to academic publications. The second part presents our researches in Geneva. The focus is put on the procedural context and its consequences on the structure and the quality of the deliberations. We present some of our results concerning the intensity of group pressure linked to the experimental conditions, together with some contrasted dynamics with debate visualizations. The third part is a discussion of the optimization of the deliberation process with respect to the expected goals. From standardization of the process for experimental purpose, to the free and comfortable expression of speech and will of the debating citizens, all the details need to be carefully considered and consciously prepared.