Here is a free guidebook of the island http://www.in-guides.com/skiathos/
You can find the print version in Skiathos at different locations as bus stations (the terminal at the harbour, Akropolis,  Agia Paraskevi and Koukounaries), the tourist information at the harbour, all ships to Skiathos from Hellenic Seaways and selected hotels and restaurants...
A nice vacation!