Challenge scaling

Bioware's challenge scaling system is meant to enable players to visit various areas of the game in a non-linear order as they prefer by automatically adjusting the levels of enemies encountered in the area to match the overall level of the player's party. However, to prevent complaints about similar scaling systems in other games (such as Elder Scrolls: Oblivion), Bioware has added lower- and upper-level limits to how far the enemies will scale in any one area. The net result is that it's entirely possible to visit some areas at too low of a level and therefore find the challenge you face to be inordinately difficult because your party strength is lower level than the lower-limit of the challenge scaling for that area. Conversely, it's also possible to visit some areas at too high of a level and therefore find the entire area not even remotely challenging, because your party strength by then is higher level than the upper-limit of the challenge scaling for that area.

Ideal order you should follow
Although the game itself allows you to visit Denerim and Orzammar immediately after leaving Lothering, you're not meant to do so until much later in the game. Unfortunately Bioware does not make this clear at all. Going to these higher-level areas too soon is a contributing factor to some players reporting that the game is "too difficult" for them even on Normal mode. Bioware meant for the Bandits outside Orzammar as you approach it for the first time to be a "gating encounter" to scare you away if you're still too low level for the intended Challenge Level of Orzammar. Likewise for the Ser Landry encounter (the duel in the back alley) in Denerim. Both encounters will be doable, if not downright easy, if you come to these areas well after level 10 as intended by Bioware.

The preferred order to visit each area based on Bioware's hard-coded challenge scaling for each area is:


 * Ostagar / Kokari Wilds > Lothering > Mage Tower > Redcliffe Village and Redcliffe Castle > Brecilian Forest > Haven > and then after all this you can hit Denerim or Orzammar in either order you prefer > then Landsmeet and the rest of the game

Note that although many players and the Prima Strategy Guide lump the Arl of Redcliffe quest arc and The Urn of Sacred Ashes quest arc together as if they were two halves of the same major quest arc, but this is not the case. Arl of Redcliffe takes place in Redcliffe Village and Redcliffe Castle, which are designed for players at level 6+. The Urn of Sacred Ashes takes place in Haven and is designed for players at level 8+. So the intended order, based on challenge scaling, is to go to Redcliffe for the Arl of Redcliffe quest arc at level 6+, then Brecilian Forest for the Nature of the Beast quest arc at level 7+, and then to Haven for The Urn of Sacred Ashes at level 8+.

As for Stone Prisoner or Warden's Keep, you can and should hit those at any level ASAP after Lothering.

For details see Challenge Scaling in Dragon Age: Origins