I always find it funny when clients show me their ads and ask me whether or not I “like” them. It is not a question of like, but whether they move votes into your corner. The main point of a political ad is to communicate your campaign message coherently and with oomph. What book coach Dan Janal teaches authors is also true for politics: get to the point, make the point, repeat the point. I therefore always suggest that you think about an advertising campaign as a series of ads, as great campaigns are rarely one knock-out punch.
Advertising is an unwelcome guest. It allows to influence people who do not care much about politics, which are often the ones to decide an election. That is why tv ads are an effective and interesting tool. The problem is that many ads are done poorly. What I mean by this is that they sound and feel like, well, political ads.
I also often observe that though some voters are not as educated as they would want to be, they are nevertheless not stupid. It is therefore important for an ad not to talk down to voters. In that sense, I am skeptical about ads which are limited to mere endorsements, entertainment, and celebrities. Also, interactions with voters should be genuine and believable. I also always advise clients to talk about their plans in some detail and to make an effort to make them believable. Voters are ready for substance.
Also keep in mind that anything you do in a campaign should either give you something you do not have yet, or consolidate something you are about to lose. If an ad simply repeats a point that all voters already know, it is not of great value.
Ideally, you would test ads in focus groups before running them (and spending serious money on the time buy). It seems like a no-brainer to me, and yet it happens all the time that candidates are so excited about their own ad that they do not bother testing them. On the other hand, I have tested ads where respondents said that it gives them goosebumps. That is how precisely the ads matched their feelings and demands.