Things to do in Skiathos?

Hi - I just joined this forum as I am going to Skiathos in just over a week with a friend.  We are staying in Skiathos town.  Could anyone give us some tips on things to do?  We would really like to do a cooking lesson, play tennis and do some yoga.  We also want to visit the island and take day trips.  I heard that Skopelos is beautiful - is it worth staying there for a couple of nights?

Any suggestions on where to go in the evening - we would like something lively/with atmosphere but want to avoid any 18-30 crowd!

All recommendations welcome :-)