Objectives have three parts:-
1) The idea. What is your mission about? What is the player supposed to do? Common ideas are destroying a particular unit, clearing an area of the enemy, meeting an ally, simply going to a particular place. However the OFP world is your oyster. If you can imagine it, it can be an objective. Probably.
2) Triggers. You need to use triggers to detect when your objective is complete. You may also need some some scripting or waypoints too.
3) Beaurocracy. Briefing.htm stuff, marking the objectives completed and all that kind of thing.
Sounds like you have stage 1 nailed down, if you are making exciting missions. If you're still having problems (this is a slightly old posts, I was going back through the forum looking for unsolved questions) tell us more specifically what's going wrong.