Periodicity
For a more detailed discussion and examples, see the "Peridocity" link.
We will be especially interested in the complex rhetorical period. A strict definition would insist that the complex thought be so arranged in cola ("clauses") and commata ("phrases") that the whole is brought to a close simultaneously with the end of the formal grammatical structure of the period. Furthermore, the thought should not appear to be merely additive, with not overarching structure of suspense and expectation. The simplest way to achieve this kind of closure is to put the main verb last.
But this is by no means the only way to create a tight or rhetorically effective period. In practice, aesthetic concerns (rhythm and balance), idiomatic concerns (that sense we all have that yet another shoe is going to drop), and logical concerns (the grammatical structure may seem to be complete, but surely there is something more to say) create any number of possible structures for tight or loose periods.
Emphasis and Enklisis
Emphasis is of two kinds: structural and substantive.
The first refers to the ordered structure of a discussion. Since connectives usually are explicit indicatory of the arguments structure, they typically go in the first position: Sed, Autem, Nunc, Nam, Ac, Tum, etc.
Substantive emphasis refers to the most important part of what is being said. It is what would be left if all else were elipted. If one imagines a sentence as answering a question, the substantive emphasis falls on the short answer: eg. "He's a queen." If this answers the question, "What is he?" then "queen" is emphatic: Regina est.
Word Order is the main indicator of emphasis.
For most words, first position is emphatic, that is, first position in phrase, colon, or sentence. For most discourse, structure is emphatic; therefore, most connectives come first.
Enklisis has the sole function of marking emphasis.
Enklisis is a subcategory of demarcative words. Some words mark the end of a phrase, colon, sentence; most notoriouly, verbs in subordinate clauses; other words mark the word they are attached to as emphatic. The second kind of word is an enclitic or is performing an enclitic function.
Predicative adjectives and participles are emphatic; they are what is, at some level, being said.
Since they are predicative, they are typically marked by enclitic verbs (especially est, but any verb) and by enclitic pronouns.