We would suggest a 6-day tour...

DAY 1 Arrival at Palermo airport and transfer to your downtown hotel. Palermo by night with English-speaking guide.
DAY 2 Full day guided tour of Monreale and Palermo highlights. Overnight in Palermo.
DAY 3 Visit the west of Sicily: full day guided tour to Segesta, Erice and Trapani (to see the salt pans). Back to the hotel in Palermo for the overnight.                           DAY 4 Leave Palermo, longway transfer to Agrigento for a guided visit to the Valley of the Temples. Overnight in Agrigento. 
DAY 5 Morning transfer to Cefalù. Visit of the medieval town and rest of the day at leisurein Cefalù. Overnight in Cefalù.                                                                               DAY 6 Transfer to Palermo airport in time for your departure transfer.