Also important to remember in a campaign is that each mission has a good story.
It can't just be a segment in the bigger picture, in the world of movie-making there are things called 'transport-stages'.
Places in the movie where you get a breather from the story and action, or places that transport the story and/or cast to different locations.
A perfect example is the very cool place in Snatch, where 'Avi' says he's coming to London. Slams down the phone, hops in the cab, flies to London, hops in a cab, BAM, he's in the office.
That's got to be one of the best transport stages that I have ever seen in my life.
Anyway, now you know what a transport stage is, those should happen exclusively
Intros/Outros and campaign-cutscenes are where to place transport stages.
Now, a movie, and a campaign too, should be built up in a specific way.
The standard way of doing it, the way 99% of the movies out t here are made, is this:
Introduce characters, story, protagonist ('Hero') and antagonist ('Badguy') and different plots (Hero1 might have a quarrel with Hero2 over who makes the best lasagna, things like that).
Tempo-raiser (My own name for it):
This is where you'll see the first encounters between the antagonist and the protagonist, or their underlings. The action and the tempo should rise in a steady fashion.
In a OFP-campaign this would best be done with escalating scale and difficulty in the missions.
So first you are part of a small squad patrolling and nothing really dangerous happens.
Then you go into a larger squad maybe with the support of another and do proper assaults and such, a.s.o. You get the point.
Point of no return (this is actually an 'official' phrase in the world of moviemaking):
This is where the hero's wife dies, or his partner, a.s.o.
Now we know there's no turning back for him before he defeats his enemy.
In OFP this would probably be a large battle to defend a position, and many of the main character's friends die. Suitably followed by the commanding officer going "We'll kick dem bastards' asses now, y'hear" or something to that effect
This is a shorter version of the tempo-raiser. In cop-movies this is where the cop loads up with weapons and goes to search for the badguys hiding place, killing lots of people in the process.
In OFP this is where the military effort is escalated and you go tear-assing all over the place.
You find the badguy and his closest crooks and you battle him and win.
In OFP this would be finding the personal hiding place of the enemy commander (The HQ should be assaulted in the tempo-raiser just before this) and battle it out with his bodyguards.
Now, that recipe is something everyone should follow. Not to the letter of course, and you can make alterations and adding more point-of-no-returns and turningpoints and tempo-raisers.
Making the story a bit more interesting.
But, something you should not forget is that each mission should follow this as well.
But for missions we could break it down into military terms:
You are told what your mission is. You are told who is to accompany you, you are given weapons
and so on.
Now, lets say there are three characters in the team which are the important ones in the main story, you should try to develop them a little in each mission.
We have Grunt, who wants to go head-on with the enemy and destroy him. "Bring me some gooks and I'll kill them" sort of guy.
Hero, which is "you", should sit on the fence so to speak. He should be able to go into "Grunt" mode, but also "Reason" mode.
Then we have Reason, who always wants to do play it safe.
Now, the mission is to assault a base.
Grunt goes: Lets fly in there with our blackhawks and bust them up.
Hero goes: Hmm, what's the expected resistance?
Reason goes: This plan sounds too dangerous to me.
Really stupid example, but you get my point. Develop the characters, and doing so you can bring important notes to the player, instead of spelling them out in the briefing.
Grunt goes "Why can't we fly in", Reason goes: "Because we have reports of Shilkas in the AO".
Now the player knows there are Shilkas in there.
This they do while they are loading up on trucks/helos/sitting in a C130 getting ready to jump/whatever during the intro mode.
The player can click past it, but it gives you the perfect material for your intro.
The intro ends when they are approaching the AO.
The mission starts with the people unloading from their transport, getting ready for the mission.
This is the peaceful part. The first tempo-raiser.
You know the enemy is out there, but not where and when he's going to strike.
Lets say the mission is to attack a village.
While moving towards it, you get radio-reports from the scouts, "We have enemy movement in the town" a.s.o.
This phase should be broken by engaging the enemy. Lets say you hit a patrol or something.
You engage and destroy the enemy patrol you encountered, but perhaps some of you die.
The squad-leader goes "Alright, they will know about us know, they must've heard the shooting, let's hurry up now so they can't prepare too much".
Everyone rushes into position and wait for the word.
The second tempo-raiser you fight the enemy in the village.
Now, if it should end here you just finish it up with the enemy being destroyed and the player taking the town.
You could add a twist however, the enemy getting armoured/airborne support or somesuch.
Now, that's the pattern to follow. Now you need to think of a plausible story.
Notice that it doesn't have to be very original, just plausible.
A four-man spec-ops team would not assault an armoured brigade for example.
The US wouldn't care about a shit-hole town on the north tip of Nogova if it had zero strategic value.
Give it strategic value ("It's the best place to post AA defenses to defend against an aerial attack from the north" for instance) and the mission to take the place would be plausible.
God I write too much.