Rdesy pretty much covered them but one I see alot is the equipment grounding concuctor cut off flush where the cable is stripped back to.
Oh and another one is the 'in mid-air areial splices', the wires twisted together and taped with friction tape the thing about it is the wires are about an 1 1/2" long,usually its a piece of old BX spliced to newer romex and of course the grounding conductors are not connected because of the two different cables.
One I see quite a bit is when pvc is used I see alot of white elbows.
I guess ignorance is bliss
