I tend to enjoy running longer campaigns that really deal with one large issue with smaller issues/excursions along the way. In the case of this group, over the course of 9 or 10 sessions I took a ragtag group who had never played an RPG and slowly introduced them to working as a party, to combat tactics, to using their skills to get around, all culminating in a dungeon crawl which will be leading to the denouement in their next session where it will be determined if they succeed or fail.
While the end of a campaign is generally not the time to think about the storyline as a whole, one of my players pointed me towards a post that analyzed storytelling as a whole and it is pretty dead on. The Rage Against The Page blog explains the natural progression of a plot via 2 different diagrams (the 4-act and the 8-point). Both diagrams describe natural plot progression of any stroy, movie, etc. and are a great way to consider the storyline of a campaign/adventure. I particularly like the 8-point because it fits very well into the natural pace of any RPG adventure from the moment the party is formed to the "end". I say "end" because both the 4-act and 8-point are both cyclical meaning one end is just the start of the next story.
The 8-point story progression (above) has, unsurprisingly, 8 points that are signified by 8 keywords (1. You, 2. Need, 3. Go, 4. Search, 5. Find, 6. Take, 7. Return, 8. Change) which all hold a much greater meaning that correlate very well to any story progression. As a DM each point will have some facets that you will have more impact on than the players, but ultimately when you look to start a campaign, you really just need to have point 2 locked down and most of the other points will start to fall into place. I'll walk through each of the 8-point story progression using the storyline of the campaign that is set to end next week.
Point 1: You
The point "you" is the point in which we find who the adventure is about. Ultimately this is the character creation portion of the adventure plus the "You find yourselves in a tavern.." start. This is where the characters are brought together to become a party, while they currently have no mission and no real direction of where to go, each player knows who they are and what they stand for and somewhat know the rest of the party.
In the case of the large group 6 of them met as they were captured after all receiving invitations to the same party, 4 of them met up with them as the 6 were emerging from the forest where they were held. All of them had been invited to the party, but the 4 showed up late. Here we have a quick overview of the who in terms that there are 10 (at the time, now 12), but mostly because I can't keep track of everyone's class and race that is the overview I have.
Point 2: Need
The point "need" is an explanation of what is going on currently and a brief explanation of what makes this world tick. Most of the time this portion is the start-up exposition that explains the world you're in, the city you're in, and the location you've found yourself.
In the case of the large group, this was simply that they had been invited to a party being thrown by the royals of Suzail (Faerun) and while heading to the party or while leaving the party they find that they've been knocked out and thrown into a cell with other members of the party forcing them to work together to get out of there.
Point 3: Go
The point "go" is the reason that the characters act. Something has happened or may happen that is driving action from the characters.
In the case of the large group, the "go" kicked in a couple times because their initial "go" was them escaping from their cell. Once they escaped from that cell though, their new "go" was going to the royals who they were invited by and trying to figure out who might have kidnapped them and why they did that.
Point 4: Search
The point "search" is following the unknown number of leads and paths to try and figure out what is going on. This point is the driving action that is directing the party around. As a DM this is where you can throw in red herrings and misdirection if you wish, or you can leave it pretty open and see where the party wants to go. Personally, I am more of a fan of letting the party decide how they want to go about the "search", but if you have a party who tends to get off track or is going way off track you can throw the solution at them to get them on the right track again.
In the case of the large group, their "search" started with talking to the king who had an errand to for the party while he found out more since the revelry had just ended. During their journey they discover an artifact hidden below a trap infested floor deep under the sea. Upon returning with the artifact they learn that the group that had captured them, the "Order of the Talon", and they had recently shown up to the area, most notably creating a situation when a member climbed into a tree boomed out a prophecy and then disappeared. Taking the artifact with them they travel up to a cathedral to find out more about a man called "Red Harvest" who had originally been found using this artifact. Their search leads to a grave of a man whom they find to be still alive, but when looking through the artifact it seems the grave was that of "Red Harvest" and it seemed to have been exhumed. They find the man across the world in Balduur's Gate and he reveals that he feigned his death to hide the fragments of a sword that was mentioned in the prophecy of the tree. He still had the pieces and give it to the party to keep it safe. They hide it in a cathedral since the pieces were supposed to return to the King who they had originally spoke to. In an effort they went to the place where the order had taken them originally and found a planar forge where the king, along with many of the order of the talon and an archdevil approached and took them captive. Now they have just barely escaped where they had been teleported and they don't know what they will find.
Point 5: Find
The point "find" is the action of fulfilling "need" no matter how it was arrived at. Since the large group has not quite arrived here yet, I don't quite have a great example, but soon they will arrive at this point.
Point 6: Take
The point "take" is a bit of a misnomer because it somewhat means what was taken from the events, but really it is the price paid and the overall taking in of what had happened. So in the situation of a standard adventure, stepping into the final battle, the "take" could be that 1 of the party members died, but you ultimately defeated the evil thus freeing the world from his/her/its grasp. It almost seems like the best description is that a major change must happen for the "take" to occur.
Point 7: Return
The point "return" is literally the return from whence you came, it could be for glory, it could be to face your past, but either way you are headed back to your origins. At this point the party would return to whomever issued the quest and collect their pay, or return to wherever needed saving and reap the glory, or perhaps even the party must return back with their heads hung in defeat as they were unable to win that tournament.
Point 8: Change
The point "change" is a time where you look at the character from point "you" and see what is different. Perhaps there is literal change in terms of maturity and growth based on the transpired events, or perhaps it can be taken in hindsight. Perhaps you could look back and say, if I knew what I did now, what would my character had done differently. Yet even still, perhaps the character's "return" point puts them in a place of great power or respect, now what actions do they have to do differently as a result of what has happened.
Looking back to the earlier part of this post, I has mentioned that campaigns and adventures meet their "end" and I mentioned how the lists are cyclical. Where it ultimately arrives at is this cycle of points can be as small as a fetch mission to as large as an entire 3-4 year adventure. I find myself treating each session or sometimes set of sessions as it's own 8-point cycle, because going to get someone a gem from the next town over and overthrowing a goblin king can will go through the same process and regardless there will be some "change". It may not always be a good change, it may not always be a large, impactful change, but the joy of roleplaying a character over a length of time is that you find that they develop likes/dislikes, tenancies, fears/suspicions based on previous events that most people sitting down to play D&D the first time rarely have.
As a DM your role in the game is to write the background and let the players write the action, the drama, and the comedy, with your assistance of course, and over the course of time you'll have found that you may have gone through this cycle plenty of times, but ultimately, each cycle will be the building blocks towards a large cycle. It seems to me that within the 8-point system, that many 8-point cycles exist in "search" until you ultimately reach the major find that begins the great denouement to the end of a campaign. Thought my large group may not realize it yet, they are about to reach that final "search" before things get crazy and things for their characters will "change" forever.