Resonance in Cyclohexenone
The structure you've drawn on the left does have a resonance structure, but not the one you've drawn on the right.



Drawing resonance structures out by hand gets quicker over time.  You find that you don't need to actually put in a "C" for carbon, or label the hydrogen atoms.  Huckel's rule generally applies to planar, cyclic molecules with continuous conjugation, although it has also be applied to transition states where an S or P orbital on a shifting C or H moiety completes a loop of continuous conjugation (for example, the 1,5 hydrogen shift in cyclopentadiene).