Campaigns typically progress through three tiers of play as characters reach higher experience levels. Each tier is discussed below.

Adventures for low-level PCs usually take place in dungeons, with little or no wilderness exploration or travel.
For the first session of a new campaign, it is sufficient to create a dungeon for characters to explore (see Designing a Dungeon). Play can begin as characters approach the dungeon entrance.
The referee might also design a base town (see Designing a Base Town), located somewhere close to the dungeon. This is where PCs can go to rest and re-equip between dungeon delves.
Initially, PCs can travel directly between the dungeon and base town, without the danger of wilderness travel.

Usually once characters reach around 3rd–4th level, they are ready to start exploring a wider area. Wilderness play is more dangerous, as PCs will not always be close to a town to rest and re-equip.
The referee should design the local region surrounding the base town (see Designing a Wilderness), placing several dungeons, monster lairs, and other points of interest.
It is best to start with a small, isolated region (e.g. an island or mountain valley), as this is quicker to design and does not overwhelm players with a huge area to explore. Once PCs have explored the local area, the referee can detail surrounding regions and the lairs, dungeons, and adventures to be found in them.

When characters reach around 9th level (sometimes known as “name level”), they are powerful enough to build strongholds and start dominions of their own. Some PCs might gain permission to rule a section of an existing kingdom, while others might wish to found a new dominion by settling a wilderness area. At this stage of the game, some PCs may retire peacefully, while others may become embroiled in political intrigues, warfare, and world-shaking events.

At all tiers of play, but especially the wilderness and domain tiers, the referee should maintain one or more plot threads of events happening in the campaign region. PCs may hear rumour of these events, or their adventures may lead them to become directly involved, whether by choice or not. The referee may design plot threads that specifically involve one or more PCs—for example, events involving their religions, guilds, families, etc.
It is important that plot threads do not lead to pre-ordained outcomes. The actions of the player characters in either ignoring or interfering in plots should remain the focus of the game.