Resonance in Cyclohexenone I don't think that cyclohexenone should have any resonance forms. Moving the double bond around would necessitate moving hydrogens around as well. For example, I know that benzene exhibits resonance (duh) and the second picture attached shows the pi bonding electrons shifting but doesn't show any hydrogens shifting positions. 





That being said, is there a easier way to determine if a resonance form of a cyclic compound is valid? Drawing out each individual atom and bond is time-consuming! Should I use Huckel's rule? Do all cyclic compounds which exhibit resonance follow Huckel's rule?
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).