In the larger destinations most people speak fluent English. In the smaller towns you can make yourself understood at least.
Travelling by bus within a city costs 17 SEK(12 SEK for children below 16), and the ticket can be used multiple times in one hour. If you are younger than 20 years old, you can buy a card called "Upp till 20"(Up to 20). With the card you can travel with bus anywhere in the county, even between cities, for a month.
Most cities and towns in the county are connected to the railway-network.
There are nothing in particular to watch out for. Pickpockets may sometime appear in crowded areas, such as popular markets and shopping-malls.