Because Sweden is above the Arctic Circle, winter can be very severe while summer temperatures are more moderate. In southern areas of the country, winter is a bit more mild than northern areas, although it still remains around freezing. In the north, summers are less extreme in the north and there is less humidity than the south.
Choosing the best time to visit Sweden depends on what you plan to do while you are there. If you want to be there when the weather is warmer, visit between May and September. If you intend to do any skiing or want to be there when it is snowing, the best time to go is late November through March. Visiting in June or July will give you the chance to see the midnight sun.
In some of the larger cities, taxis are very easy to find, even though they can be a little expensive. There should be a yellow fare sticker inside the cab and the average cost is around 300 krona. Any higher fare is too much and you can just walk away in order to find another taxi.
Gothenberg and Alvsnabben have regularly scheduled ferries. Stockholm uses water taxies during heavy tourist season. There are also a few water taxi options between Sweden and Germany, Finland, Norway, small Baltic States as well as Poland.
There are some cities with public trains and buses with Stockholm offering the most efficient system. There are four lines that connect to the center of town as well as many bus lines that are reasonable. There are some bus lines that operate between cities, although most originate or end in Stockholm. There are also train routes to Germany, Finland, Norway and Denmark, most at a fairly reasonable cost.