Try the following items to shake things up.
- Everyone has an objective, total annihilation of your opponent rarely is the real one
- Very few creatures will actually suicidally fight until they are dead or their opponent is dead. They will often flee when it looks like they don't have the advantage
- Fight for something. Maybe you are just trying to steal something and get out, or just assassinate one of many characters.
- Have some dynamic locations, maybe a rolling ship or a place that has moving mine carts or lava flows.
- Have the battlefield change somehow during the fight. Maybe a wall falls down that suddenly has a lot of men with guns on the other side. Maybe a super powerful cannon is revealed halfway through that changes the tactics
- Give environmental hazards. It makes combat a lot more interesting when you are trying to knock each other off of airship platforms than just trying to club each other over the head. This gives you a chance to use special rules like grappling or pushing
