First of all I'm no expert in mission building but have discovered some things along the way and thought I might share them with you. As I go along I'll add what I can.
1. Aircraft- When placing altitude lower that 1000m (say the default 500m) for Dive-bombers and level-bombers they will react in a weird way, in that physical movements appear unrealistic, eg. at 500m or lower they will most likely crash or raise up to the sky and stall. At 1000m or so they react much better and won't be shot down like flies. They hit their targets much better too. Torpedo-bombers should be set at 100m-200m.
2. Do not add any naval bases where they are historically located on the game's map. It's already there.
3. You have to disable the hand icon for you to do any addition of waypoints, objects, etc. Believe me it took some time to figure this out.
4. Sometimes when you set a map zone and set a time for, say, a message to appear it sometimes do not always come at that set time, eg, I had set up a zone in such a way that when I enter it and after 1 minute I would get the message. However,an additional 2 mins had passed when I got the message whilst inside the zone. Maybe it's a game bug, I don't know. Zones are really neat in the editor.
5. If you want ships stationary at say a dock or base then set the object close to the area where the dock or base is (unfortunately bases are not depicted on the editor map- I had to guess an approximation and trial and error to place objects in the right position. There is a way I believe using the merge option). Set the speed to 0 and set a waypoint for it and tick the dock box. Make sure to orient the object just the way you want it by using the heading box.
6. Want to move a convoy or group attached to a main object? Move them on the editor map one by one? Nah, ensure the move hand icon is disabled and outline a box around the objects. Now you can move the whole group.
7. When setting subs do not place the height level greater than 0 or else you won't have a sub but a plane.
Ok, so I'm not Einstein. Just some things I picked up along the way. Some or all may be known already and regarded as basic. I'll post up some more tips as the come in hand. Cheerio!