To me, TOS thematic elements include:
1. Characters solve the problem despite technology: Technology is often an impediment in the story, and the stars of the show often succeed despite it, rather than because of it.
2. Creative skirting of the Prime Directive: Put the stars into a situation where the Prime Directive is in place, but give them a moral imperative to justifiably act despite of it. In a broader sense, this could be seen as Starfleet regulations as an impediment to successful resolution of the problem.
3. Nothing beats a good fist fight: Throw one in for good measure.
4. Cold War Klingons: Klingons are more like Soviets than the samurai vikings of TNG and beyond.
5. Captains as action heroes: Of course, the stars of the show should always go on the landing parties and be at the center of the action. This might be more difficult to pull off if you have a full ensemble.
Davy Jones
"Frightened? My dear, you are looking at a man who has laughed in the face of death, sneered at doom, and chuckled at catastrophe! I was petrified."
-- The Wizard of Oz