how can an ads be effective?

[Robert M.]

This topic can be the subject of intensive semester courses in b-school marketing, and there's no Yahoo Answers size wrap-up that would be fully meaningful, aside from the usual truisms about memorability while retaining clear product or brand recognition, etc.

Better if you gave us the product and perceived market, target demographics, 'house style', philosophy, and mission of the advertiser, etc. That would enable me to winnow down 'effectiveness' to the target market(s) and potential clientele that matter most.