Starting from Ahemdbad(food& culture) -- Diu(beaches& peace)-- Somanth( temple) Porbandar(Gandhi's home) -- Dwarka( Krishna's kingdom)-- Bhuj( white desert). you can cover all the places in 6-7 days or can choose few of the places for 4-5 days trip but the best time to visit Gujrat is in winters, especially for white desert in Bhuj which is magnificent. Otherwise Sept onwards is also good but to visit in July- August you should be ready to bear the harsh temp.
There are multiple places. You can visit Rann of Kutch ( Would be more feasible during winters), Akshardham temple in Gandhinagar or Surat beach. If in Ahmedabad, go for Nalsarovar bird sanctuary, Sabarmati riverfront, Sabarmati ashram, Kankaria lake, Adalaj Stepwell. There is statue of unity, Dwarka and Somnath temple too.