There are a limited number of ways one can write an adventure. Let's start with the famous railroad model:

Choo Choo!

PCs Get a Quest
Part 1
Go to Part 2
Go to Part 3
Go to Part 4
Go to Part 5
Boss fight

The tell-tale signs you'll find here are sentences like 'when the PCs reach the village', or 'when the PCs find the item'. Basically, anything beginning with 'when the PCs...', because that's making an assumption about the players' decisions, and that assumption will push the GM into making sure the PCs follow through with the suggestion.

The entire structure's a classic trap people fall into from watching films, or playing computer games, and classically, it does not produce an interesting game.

The Art Show

An art show lets people in one entrance, has a bunch of things to see, then spits them out the other side.

	PCs Get a Quest
Encounter	Encounter	Encounter
Encounter	Encounter	Encounter
	Boss fight

One example here is Return to White Plume Mountain, which locks players into a quest to avoid a magical curse, then allows them to wander the tunnels of a mountain freely. However, the only way to break the curse is in a particular area, deep inside the mountain, so the players must eventually explore this area.

The Festival

At the festival, you can see some attractions, but the real events happen at particular times, so the story itself decides the pace of the adventure.

	PCs Get a Quest
Day 0	Location A	Location B
Day 1	Encounter 1	Encounter 2
Day 2	Encounter 3	Encounter 4
Day 3	Encounter 5	Encounter 6
Day 4	Encounter 7	Encounter 8

One example of this is Trouble at Grogg's, an adventure where the party can wander town, but the plot must develop over time as thieves sneak, steal, and burn things down around them. This adventure was unique for its time as it had no ending. When reading, it seemed to just end with a flaccid absence, but when playing the thing, a natural ending emerged from the knowledge the PCs had developed so far.

Side Quests

The Side Quest system in the game is mostly based on 'The Festival' approach, with events coming at the players, rather than any notion that players might be required to get somewhere on time. Various small plots are mixed together, and each part of a plot is placed in a different area. The areas are important, because players must be free to wander different places. 'A', 'B', and 'C', could be 'Desert', 'Sea' and 'Town', or any other large areas.

Area A	Area B	Area C
Encounter A 1	Encounter B 1	Encounter C 1
Encounter B 2	Encounter A 2	Encounter C 2
Encounter A 3	Encounter B 3	Encounter C 3
Encounter A 4	Encounter D 2	Encounter D 3
Encounter D 1	Encounter E 1	Encounter E 2

If the players enter area A, they get encounter A, part 1. After this the next available 'part 1' is Encounter D, part 1, so that's what they get. If, on the other hand, they enter Area B, they'll get encounter B, part 1, then the second part of encounter A (which they already started). This means B2 is active, as well as A3.

The whole tends to be a lot of foreshadowing, and players saying 'remember he's from that time when...'.