I don't pretend to offer the last word on this elusive concept, but I do offer here four principles for improving flow in your writing, your research paper included. When you understand the big question you're answering in any piece of writing, you can figure out what questions must precede it and which follow from it. Any claim I make about fixing the electoral college, for example, must first answer what's wrong with it.
Parallel structure involves repeating subjects in consecutive sentences.
Parallel structure involves repeating verbs, linking phrases, copying clauses, part for part, as I have done in this paragraph. Parallelism works because it creates anticipation in readers, who can see where the argument is going simply from the repetition of key words. Parallel structure works across paragraph boundaries too. Such repetition matters particularly in an oral setting, which is why Jesus used it and why today's politicians do the same. The heart of the sentence lies in its subject and verb.