Missions and Campaigns should be built considering the player for the most enjoyment and excitement.
It needs to be emphasized, the player must be the focus of missions from start to finish. Several things should loom large in your thoughts as you build missions.
Action events in missions should occur when and where the player can enjoy them…
It doesn't benefit the player for action going on all over the map, when the player is somewhere else.
When you build your missions you should think about some of the items listed below:

1. The player should never be tied down in an escort role, this is a job for AI. Never stick your player to turning circles to escort.
2. Find something for your player to be doing that is best for enjoyment of the mission The player can fly a different route and meet up with the escort group where the action occurs.
3. Advise your players in your readme to select a rank that places them properly within flights. If the player is following the AI around, remember your player may get shot down and not have a chance to complete the mission and advance. The Ai do some world class stupid things. It won't take your player long to get the hang of it.
4. Keep your player interest by getting the action going, seven (7) and not more than fifteen (15)minutes for your player to enter action. If your action area is a greater distance away make a point to have a straight run at it. This way your player can 8X to your action area.  It is important to remember, if you drag out your missions your player will 8x your missions and get bored with your campaign very quickly. 
5. Weather is a fun thing you would think. Nice clouds do add a lot to the experience. If your player is in a campaign and must complete the mission to move on in the campaign; weather can be bad. Weather and Clouds can be a powerful detriment, because your player is handicapped visually. The AI is all seeing, therefore the player is at a serious disadvantage in bad weather when visually impaired.
6. You might think to apply weather when your player won't be engaged in a tough dog fight. Apply the weather and clouds on missions that won't advantage the AI against the player.
7. Night flying sounds cool, but has it's drawbacks. If you want to add night flying you might think to have the tough part of the mission while there is still enough daylight for action engagements. Then when the player heads for home and the sun goes down you need to have a well lighted (barrels or lights) runway for the player to finish the mission.
8. Ground action items should be timed to work when the player is in the action area. It is a waste of good FPS to have ground vehicles moving all over the map, except when and where they are needed.
9. It is difficult to apply tactical flying in IL2, but there are workarounds. One workaround that helps is to have your AI attack opponents by using a SET in the FMB. In other words, do a set waypoint attack from your AI to the enemy and a set from the AI enemy to your friendly AI. This way they will go to work on each other full out.
10. It is generally best in campaigns to set your enemy AI skill several levels below friendly AI skill levels. It is good for player to have a better chance of advancing and coming home with a victorious flight group.
11. If you are building missions(not campaigns) to test the skills of your player you can make the skill levels as you please.
12. Campaigns shouldn't be as tough as individual missions. You don't want your player frustrated by having to re-fly a mission several times. Again, remember it's about the player enjoying his experience in the campaign not testing his flying skills to some extreme level.
13. Ground objects add a tremendous amount to the immersive experience, yet there can be too many objects in all the wrong places.
14. When the player takes off and lands it is important to have objects and vehicles stationary and moving in very close proximity of the player at the time the player is in that precise place. All the objects scattered around an airbase are fine at enemy airbases where the player is attacking or engaging the enemy.
15. The huge arrays of objects around a friendly airport are useless for the most part, because when the enemy AI attack all you need is a few buildings and aircraft to pop in close proximity of the player for the player to get the full enjoyment of the action.
16. Think to use moving vehicles, noisy artillery, campfires reflecting off aircraft and vehicles, etc. to make landing and taking off feel like a bustling war atmosphere. Place these types of objects close to the runway always where the player can view and enjoy them.
17. A bunch of trees placed around an airbase is a waste. Use things that create action in the mind of the player not a bunch of palm trees surrounding the airbase. The airbases are flat and dead with stationary objects. Remember, moving stuff that the player sees adds to immersive feel of war.
18. You have probably flown campaigns where you are constantly changing aircraft. This can be fun, but it's far from anything realistic. WW2 pilots were checked out and qualified to fly specific aircraft. Pilots flew what they were officially qualified to fly.
19. It isn't boring to fly the same aircraft or new model of the same aircraft during a campaign. Make a new campaign, if you want to provide a different aircraft.
20. Historically based campaigns should be time defined, a squadron ID selected, and the aircraft of the player and enemy should be very closely timed to have actually flown in battle at the same time, against each other, at the specific place. This makes for some real excitement and makes a lot more sense than flying late war Spits against early war 109s.
21. It is important to respect the time of your player.  How many campaigns have you flown where you were constantly in the queue to land and were bypassed continuously.  When you are in a campaign you cannot get points or continue unless you complete your mission.  It is not uncommon to fly a holding pattern for twenty minutes.   There is a solution, and that is to use the Recon-Target tool in the FMB setup on the landing airbase of all missions in your campaigns.  There are several ways to get mission completes, but this way your player will have to complete the entire mission and fly across the end of the landing base runway to complete the mission.  It helps to maintain a feel for realism without the player having to fly a landing pattern for twenty minutes to land.
22. http://www.avsims.com/CFS/content/using-recon-target-il2-fmb-terminate-missions

I should add there are other ways to enjoy IL2 missions and campaigns. The ground cameras can be fun to watch and replay of video tracks can another. I've frequently just run a campaign and put the player on autopilot. This way I hopped around between the player flights and enemy flights and watched the air battles from many viewpoints.