Something that is effective produces a desired or expected result. Something that is potent is not just effective; it's powerful. Potent implies great natural or inherent power, and it works as a synonym for effective when applied to things that are highly persuasive or convincing, such as a well-constructed argument. Potent symbols and potent metaphors are powerfully evocative, and potent ingredients produce powerful physical or chemical effects.
Something that is valuable has considerable monetary worth or is particularly useful for a specific purpose. This adjective is often used to talk about things that offer or may one day offer a material advantage or quantifiable benefit. Something that is invaluable has value beyond calculation or appraisal; it is priceless. Here we get into things so important or meaningful, such as the support of a dear friend through a difficult time, or yielding benefits of such great magnitude that they defy measurement or estimation.
Something that is common is widespread or universal. Something that is prevailing is generally current and supersedes others of its kind. The key difference is the suggestion of predominance. For instance, a prevailing view on a matter is a view that has taken over or displaced other views. A prevailing fashion is one that has caught on and emerged as the most notable or influential at a particular time.