The nomenclature that comes with the drug suggests taking it 30-45 minutes prior to sexual activity. Notwithstanding, Cialis works for up to 36 hours, so... if your activities include a meal, I propose taking just before you eat.
As a general rule of thumb, taking any medication on an emtpy belly will cause the effects to take place a little sooner and a little more pronounced. In the case of this medication id think that might be a good thing ) Just make sure you take it with plenty of water, as with any medication.
Common sense tells me you dont want to have sex on a full stomach, you might throw up