Most of these can be fixed quite easily. Usually a renaming of a character or item will solve a problem. Sometimes it's necessary to provide a secondary character viewpoint so that a scene's importance to the story can be understood. Make sure that you are writing a unified work. Don't start out writing something depressing and then change to a funny scene unless you know exactly what you are doing.
Swords are cool, but almost totally useless for any encounter in science fiction.
The other guy probably has a gun, and the guy with the gun always wins in such a contest. However, when wrestling for control of a sword, the person with the handle always wins. Tactical errors will turn off a reader fast. Try to foreshadow what will happen, but don't be too obvious. One book I read, I realized exactly what needed to happen in the story out of the first fourth of it, and the rest of the story followed almost exactly what happened.