It is very common to give a special introduction to the Sarek Parek in every book or magazine dealing with Lappland. In my opinion, the best of the introductions is given by the Swedish "Naturvardsverket" in the paper "Sarek - Myth and Reality" that you can get for instance in the Jokkmokk Tourist Information.
It points out that the Sarek Park will be protected from human influence more than other National Parks in Sweden, and that nothing will be done to make backpacking tours easier. Trails exist, but they are not marked. Very few huts exist, but they are locked and were built for scientists or reindeer herders. The weather can be very bad, it rains a lot and can have snow even in the summer. This can as well happen on a marked path, of course, but then it is easier to warm up in a hut or shelter. There are some bridges; without them a tour across the Sarek would be nearly impossible, but a lot of rivers have to be waded, which is sometimes difficult.
Some people even do their first backpacking tour at all in the Sarek National Park, but if you don't have experience, without a doubt it will be better to chose a tour on one of the well known marked trails like Padjelanta or Kungsleden, and learn a lot about the conditions.
However, when you have hiked most of the trails around the Sarek Park and want to see still more, the Sarek will probably attract you very strongly. There are easier tours, where you stay in the valleys and don't go over passes or glaciers, and more difficult ones. One should study the BD10 map thoroughly and read all kinds of informations, however, much less descriptions exist than for the marked trails. Surely , I'm not one of the Sarek experts, but I try to describe some basics that you need to know when you read the map.
Locate the bridge across the Smaila river in the sketch of the Sarek Park. It is a central point for many reasons. Without this bridge, most north-south and east-west tours would be difficult or impossible. You find good campsites in the whole area around Smaila bridge, a help telephone at the locked Mikkastugan and even a toilet. During season, you will meet other backpackers here at this crossing of trails as well as people doing day tours from here to one of the summits. Therefore, swedish hikers call it Smailaträffen, that means meeting point.
You can reach the Smaila bridge from Aktse along the Rapadalen, from Rinim through the Pastavagge, from the Sourva dam over the bridge in the southern Kukkesvagge and from Kisuris through the Ruotesvagge. These are easier tours (perhaps not easy tours, but easier than some other tours in the Sarek). Three of these are indicated on the BD10 map as unmarked paths. Normally it takes about two or three days to reach Smaila bridge from outside. To go in and out, you can chose a combination of two of the tours, which makes four to six days, if everything works fine. For the Kisuris - Rinim trail, it is mentioned in the paper of the "Naturvardsverket" that the Tjagnarisjakatj, a smaller river a few kilometers from the Smaila bridge, can be difficult to wade, and that sometimes snowfall occurs in the Pielaslätten area. I would mention in addition that the Pastavagge is 1066 m at the highest point and sometimes is obscured by clouds.
From the Smaila bridge to the west you can go through the Alkavagge and the Kuopervagge. The Alkavagge tour can bring you to Staloluokta and the Kuopervagge to Kisuris, for instance.
From the south, you can enter from Kvikkjokk via Pareks sameviste and hike either west along the Njatjosvagge (indicated on the map) or east to the bridge across the Katokjakka. From the bridge you can reach the Sarvesvagge. These tours include higher elevations and are more difficult. Since I don't have own experiences with them, I just want to mention them.
Finally, it is to mention that most of the deadly accidents happen when hikers wade the rivers. Therefore, you should be careful, observe the rules on the posters in the huts on the bigger trails, know about the bridges and use the newest maps.
For more information on the Park , try the server of the Naturvardsverket http://www.environ.se/park/natpark.htm (in Swedish). A few descriptions of Sarek tours are to be found in "Utsidan" at http://www.utsidan.se. Concerning the tours on my pages, I can answer emails, if you have special questions.
Have a nice trip all the time! ....