read more about allemansrätten, http://www.naturvardsverket.se/en/In-En … ic-access/
http://www.naturvardsverket.se/en/In-En … tor-homes/
it is basically legal to park anywhere and sleep over. as long as you do not endanger others or destroy stuff. you do not need to stay at a campground, it's wasted money. There are many parkingareas along the road and often real flush toilets and water. if you find a parking space on a 24h open gas station, for example, they can find it disturbing that someone sleeping on their parking so they may ask you to leave, so tip is the park at a lake shore or sea or similar. there are usually signs that say if you can camp there. remember not drive on the beaches or sand, without permission. but park on a grass parking next to the beach is allowed.
leave the place as you wish to find it, I think is the main rule.