Travelling from most locations, it is best to book your flight to Visby during the month of October for the best deal, although there are other times of the year which offer great deals as well.
In general, booking your departure to Visby for a Tuesday represents the best deal on airfare. Try to avoid a Thursday departure to stay away from the highest prices.
Generally, when visiting Visby, afternoon flights represent the best value. midday flights are likely to have higher prices.