Folks say that you should compare Apples with Apples and compare Oranges with Oranges. As it relates to Trademark Law, these comparisons can determine the relative strength or weakness of a Trademark.
One example of a weak Trademark is an "Apple Store" if this Trademark were used with a fruit stand which primarily sold apples. This is a weak Trademark because the Trademark "Apple Store" names or closely describes the goods: apples. Moreover, a Trademark such as the"Red Apple Store" would only be slightly stronger and enforceable because the word "Red" actually describes the apples in to be sold. The underlying principle of Trademark Law is to prevent businesses and individuals from monopolizing general words which would prevent others from naming or describing the goods which are to be sold.
Make the Comparison
An example of a strong Trademark would be Apple(R) Computer. Apple(R) Computer is a very strong Trademark because of the unlikely juxtaposition between high-tech gizmo with gigabytes, software, and geek-speak and fruits. This unlikely combination between the word "apple" and the good it is to brand (computer) makes the Apple(R) Trademark strong.
What are the benefits of having a strong Trademark as opposed to a weak Trademark? In the previous example, let's assume that "Apple Store" is given some Trademark status with respect to a street-side apple cart in a farmer's market. Because the "Apple Store" Trademark is a weak Trademark, a competitor may compete under the Trademark "Red Apples Store" and would likely not be in violation of a Trademark infringement dispute. Generally speaking, the weaker the Trademark, the closer a competitor can come to it without creating actual infringement.
Compare your goods/services with the Trademark
Regarding the Apple(R) Computer Trademark, a competitor would be liable for trademark infringement if they were to market computers as Green Apple Computers. Because the Apple(R) Trademark is strong, Trademark Law will not allow businesses from using a Trademark on computers and attendant products and services which even remotely resemble their Trademark. Another example might be if a competitor were to use "Manzana Computer" (manzana is Spanish for apple), "Ripe Apples Computer", "Apple Pie Computer", etc.
Businesses are in a stronger legal position as it concerns Trademark Law to create Trademarks which do not name, describe, or imply the goods or services with which they desire to use the trademark. If you would like a stronger trademark you should consider a trademark which is fanciful and arbitrary. Or, in the alternative, use a word mark which hints at a particular quality of your product.
Use common sense in conjunction with Trademark Law
For instance, if you are selling perfume, the word mark "Mystery Blue" may imply, or conjure up images of desire, inhibition, sex appeal, etc. which may give a prospective consume an idea of what your product is and simultaneously describing in vague, but potent terms certain qualities, values, or images which you desire to imbue into your word mark.
Of course, there may be times when businesses may have to use descriptive or generic marks where necessary in order to reduce advertising or marketing costs. As such, business owners are cautioned to balance their own marketing needs with the fundamentals of Trademark Law.