This tip may sound absolutly nutz, but it does work.
If you have a small amount of flash on your plastic parts, like the windows that Chuck is talking about, you will notice that this flash is transluscent. In other words, thin enough that light can be seen through it but still you can't make out what is on the other side of it.
Take a brush full of your liquid plastic cement like Ambroid, Tennax or Testors in the bottle, and brush it on to this flash. It will melt away like butter in a hot pan. Try it some time and let me know how you like it. The finish is much smoother that any filing you can do. Remember, these glues soften the plastic to make a bond. That's why it works to melt the flash away.
B-)