Which resonance structure would be favorably contributed to the actual structure?
(a) Positive charge on $\ce{C}$ versus positive charge on $\ce{O}$: Even though $\ce{O}$ is more electronegative than $\ce{C}$, its octet is fulfilled while $\ce{C}$'s is not (only 6 $e^-$s on positively charged $\ce{C}$). Therefore, second structure is more favored over the first one.
(b) Negative charge on $\ce{O}$ versus negative charge on $\ce{C}$: Here, both negatively charged $\ce{O}$ and $\ce{C}$ have their octet fulfilled. Yet, it is always stable when the negative charge is on more electronegative atom ($\ce{O}$) than on comparatively less negative atom ($\ce{C}$). Therefore, first structure is more favored over the second one.
(c) Positive charge on $\ce{C}$ versus positive charge on $\ce{O}$: Here, same argument of (a) applied here. Therefore, second structure is more favored over the first one.
(d) Charge separation versus neutral: it is always stable when the compound has no charge (neutral) than on has charge separation (with net charge is zero). Therefore, second structure is more favored over the first one.
(e) and (f) Kekulé structures of naphthalene and benzene, respectively: Of each pair, first and second structures have the same energy. Therefore, both structures of each pair have same stability equally favored.
(g) Positive charge on $2^\circ$-$\ce{C}$ in both structures: Since positive charge is on a $2^\circ$-$\ce{C}$ of each compound, the relative energy due to carbocation is same on both structures.  Yet, the first structure has its double bond conjugated to the carbonyl carbon while the second structure has isolated double bond to the carbonyl carbon (cross-conjugated). Therefore, first structure is more favored over the second one.