To counteract this, I try to kick off a sentence with action. I love action-oriented writing anyway, so this is perfect. It goes something like this: "Leaping to his feet, Jim ran to the door."
Another way to break up sentence structure is to be more descriptive. Every single thing a character says or does is an opportunity to build up more story and interest in the character, so don't squander it! You could give a simple action more punch like this: "With a scowl on his face that could melt ice, Jim leapt to his feet and ran to the door."
Same guy running to the same door, but now we've got emotion built into it. Of course, you can also fill out the scene a bit more by describing the tension in the room before Jim jumps to his feet. That would let the scene build up before he jumps up and runs off. Or you could add details like "Jim leapt to his feet, overturning his chair as he raced to the door." I find it's easy to overdo that kind of thing, but it's great if you use it in small spoonfuls.
That's enough for now. Go write something! Just a paragraph. Go. Begone.