You want to file a very short trademark with a word or two. But there’s a problem because a similar mark is in use, or your brief filing is merely descriptive. 

Should you add elements to your trademark registration to make it registrable?

Possibly, but there are two sides to that answer.

First, the answer is yes; the more elements, the more registrable your trademark becomes. For example, let’s say you are a software company wanting to register a trademark containing the name Microsoft. Your trademark name search will tell you it is in use, and you cannot use it in your trademark.