It is best to observe Ekadasi vratam without even partaking water. If it is not possible, one can take liquid food or fruits; even if that is not possible, one can take light tiffin but one must certainly avoid cooked whole rice at any cost.
One should break the fasting next day on Dwadasi by doing Aradhanam for Perumal and Padukas, partake Perumal and Paduka tirtham, offer food to Perumal and partake prasadham during Dvadasi Paranai.
During Paranai one has to do parishesanam to plain cooked rice with ghee (cleansing of cooked rice) and add saltless sundakai fried in ghee, agathi keerai and nellikai to the cooked rice and partake them to complete the vratam.
It is considered superior if these can be consumed raw if not it can be sundried.
Fasting should be completed within the Paranai time.