The pot should be as small as the root ball. The more root bound, the likelier you are to get fruit. They don't respond well to having luscious soil nor plenty of it. Well, no they do respond, they just get big with loads of leaves, the fruit is sacrificed.

From my Contained Garden book:
Ficus carica - pot size 30cm/12 inches wide by 25cm/10 inches deep. Use a mix of John Innes No. 2 and good multi purpose compost, or just John Innes No. 2. In early summer, prune strong, young stems to leave four to six leaves, providing these stems are not bearing fruits. Fruits will form in leaf axils on new shoots. Do a light winter prune (not sure what that means) and remove any inward growing branches in spring as well. Water frequently in Spring and summer. Apply liquid feed weekly when fruits are swelling.

That works best with a semi-dwarf variety such as 'Brown Turkey' or 'Black Jack'. Bigger varieties need to grow at least a 30 cm a year to bear fruit, and need larger pots, 70-100 cm wide and deep.