The perfect word
One of the under-appreciated skills of the best copywriting is the precision of the wording, especially in headlines. With so much of current "professional" advertising falling into labored attempts at humor and wordless visual puns, it's good to remember to power of, not just words, but well-chosen words.
In the ad above, created sometimes during the '60s by the agency Papert Koenig Lois, George Lois recalls that the initial inspiration for this ad's headline read this way: If your Harvey Probber chair is crooked, straighten the floor."
See the difference. In its first generation, the headline is somewhat at odds with the client's message of precision-built furniture. The phrase, "If your chair is crooked" implies that the defect is in the chair. Changing the wording to "If your chair wobbles" is more neutral towards the chair, and helps reinforce the idea that the floor is at fault.
Incidentally, the heavy red/brown color scheme of the ad (reproduced a bit too darkly here) was also precisely chosen, to direct your eyes to the matchbook under the chair's leg.