How do I figure it out? I ask people who speak Hebrew. Obviously, it was Hebrew that the English version you have available to you was translated from (I hope).
And Hebrew roots, colloquialisms, traditions, and common phrases are all important to understanding the language we sometimes see translated either word-for-word or paraphrased, but hardly ever both.
The line is drawn by what a Jewish scholar will tell you. Or a Greek scholar if it's a question about a phrase in the New Testament.
There is only one way to properly understand the bible in your language and that's simply a word called, "hermaneutics," or the method of studying scripture.
I believe it is from Hank Hanegraaf where I got a better understanding of how exactly the bible is read logically.
For example:
The Literal Principle of Hermanuetics states that what is intended to be taken literally should be taken litearlly. For example, the story of Adam and Eve. At first glance there is nothing to indicate that the writer intends this story to be anything but a simple true story of two real people.
The Figurative Principle states that what is meant and intended to be taken as a figure should be taken as such. A vision of a dragon sweeping a third of the stars to the earth is just that: a vision. It's not a real literal dragon flinging real literal stars on the earth (we'd all be burned to a crisp!). Later on the stars are explained to be a third of the angels that fell with Lucifer. What is meant to be taken figuretively should be taken as such.
These two principles are the beginning of five principles to help anyone gain the understanding of any perspective in the bible.
The other princples are:
Historical Princple - take things in their obvious historical context.
Grammatical Principle - metaphors, colloquialisms, phrases and sayings should be taken in context and understood.
Harmony Principle - everything interpreted from scripture must harmonize with anything literally true in scripture. In other words, no contradictions are allowed in interpretations blatantly contradicting stated and clear scripture.
Following these princples, anyone can "draw the line" and indeed follow it.