Mixed constructions occur when parts of a sentence don't fit together. The example sentence has two parts, a subject part (because he raises questions) and a predicate part (helps readers relate) that don't fit together. What is it that "helps readers relate"? We don't know since the first part (because he raises questions) can't serve as a subject. You can change either of the two parts.

Correction #1: Because he raises questions, readers can relate. (Now the verb in the main clause has a subject.)
Correction #2: Raising questions helps readers relate. (Now the verb "helps" has subject, the gerund "raising.")

If English is not your native language, the example sentence may sound fine to you. If this is the case, there isn't any easy way to develop an ear that is better tuned to the sound of correct English, but a program of reading aloud several minutes each day on a regular basis can help.

Check the following resources for useful practice material: 1) Guide to Grammar and Writing, 2) Colleen Hildebrand's UCI Correction Symbols with hyperlinks.

For more information on mixed constructions, visit the LARC Electronic Writing Center Grammar Checklist.