Dragon Age: Origins has several main quests which have to be completed in order to complete the game.
Main quests
Lothering and the Imperial Highway
Ideal order
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 Bounty Hunters 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. However, lower-level players may find these location rewarding in both experience and higher-tier items.
The preferred order to visit each area is as follows, based solely on the lower and upper limits of BioWare's hard-coded challenge scaling for each area. It is of course perfectly legitimate to follow a different order for roleplay reasons or because you want to add a specific companion or items to your party sooner. However, you might find that some areas are too difficult if you visit them too soon, and conversely some areas might be too easy if you visit them too late. For example, Redcliffe Village/Castle has an upper limit of level 10–11 for normal enemies and below, level 12 for lieutenants, and level 14 for bosses.
- See Challenge Scaling in Dragon Age: Origins for details.
- Ostagar and Korcari Wilds
- Lothering
- Circle Tower
- Redcliffe Village and Redcliffe Castle
- Brecilian Forest
- Haven
- Denerim and Orzammar in either order you prefer
- Landsmeet and the rest of the game
The Circle Tower is best done first for two reasons: You reap the early-game benefits of acquiring permanent stat boosts from essences and fonts found throughout the Fade during the Lost in Dreams quest; and you can recruit the dedicated party healer there and at a certain point in the Redcliffe Castle later on, you can get the mages' help with the quest.
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, 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 The Stone Prisoner, Return to Ostagar, or Warden's Keep, you can and should hit those at any level ASAP after Lothering (or you may opt to visit at a later level if you want to get the highest-grade Warden Commander Armor Set, though, as its quality is level-dependant. However, if you want to upgrade the W-C Armor simply drop it in the Party Storage Chest and come back to get it at a higher level. The same rule applies for Cailan's Armor Set. All items acquired in Warden's Keep or Ostagar are scale-able items. After finishing these quests, you will still be able to return to Lothering (in case you need to buy certain items or complete unfinished quests). You won't be able to return to Lothering when you finish any of the main quests.
Another option is starting Orzammar early for the Key to the City "ring", giving +2 to all attributes. You need to have a group strong enough to take out the bounty hunters and then Loghain's embassy at the doors of Orzammar. As experience shows, it can be done directly after Lothering. You can finish it later.