Hi...do you want to make missions like real professionals??? Then u need to refer these few tips :

1. Download and play the missions created by Senior and experienced designers...you might get a lot to learn from those missions.

2. Spend considerable time toying around with the DYOM menu..maybe u will discover new things.

3. Use readable language while using text in cutscenes and other objectives..

4. U can use helpful tools ( in DYOM menu ) this will make mission designing easier..

5. AFTER ALL THIS you are ready to design your own missions..best of luck!