As GM, design of a combat encounter is critical. Here's my design template:
1. Combat motive - why are parties involved willing to / resorted in fighting each other? Provides frame for combat objective.
2. Combat objective - what is the goal for each party in terms of combat result? Buy time, run away, capture, kill, humiliate, incapacitate etc.
3. Combat strategies - what will the enemies try as their main and alternative strategy, will they try to keep their distance or charge head on.
4. Non-combat objective - during combat there can be a non-combat goal such as raising a draw-bridge, setting fuses, escorting civilians to safety etc that is targeted with maneuvers mainly and greatly affected by how characters are positioned in combat.
5. Location - don't fight in empty space but great obstacles, lighting effects, different elevations, perilous traps, stunt requiring maneuvers like swinging on a rope etc.
6. Events - what happens when either side is getting on top? How does a character death affect the battle?
(...)
Whatever you do, consider that each combat event is an investment of 30-120 minutes of playtime in average and should be designed to be thrilling to the end. If you see it continuing for too long - use an event to cut it short. If it seems to be over too fast and unwantedly unexpected - use another type of event to continue it for a few more rounds.