After you finish your model, you'll need to take a few moments to verify that the geometry is clean. Clean geometry means:
No coplanar/coincident faces. This means faces that occupy the same space, which will cause flickering during animation. It is fine to have intersecting faces that cut through one another.
No overlapping/coincident vertices (vertices that should be welded but aren't).
Normals facing out.
While your modeling practices probably prevent these problems most of the time, checking your models is easy and takes just a few minutes.