The best time for traveling is May/June when the whole island is in blossom and September, when the sea is still warm, the mountains not yet in snow and the rush of the summer months is gone. Also October is still pretty good but it can already be rainy and stormy.
The summer months are pretty hot and dry. The winter months are humid and not that cold, at least at the coast. In the mountains, winter can be pretty cold and there can be snow as well.