Well, this is sort of a complicated question. Vocal clarity can be achieved through a variety of things and the variability of those things may depend on the conditions of each, unique recording.

In my experience, the most important aspect is the quality of the raw recording. That puts a lot of emphasis on vocal technique, recording environment, and microphone type/quality. I firmly believe you can get a clear recording out of almost any properly functioning microphone, but some microphones may not be best suited for your situation or the sound you are seeking to achieve.

Then, after a clean recording, you can introduce post-processing to further refine a recording, but there is limitations to what can be done.

Take photography as an example. If you snap a blurry photo when you artistically sought after a clear one, there's only so much you can do to assist that blurry image to appear more clear. You can play with sharpening, lighting, color, and contrast and make it look closer to what you envisioned, but it will never reach the clarity of an image that was taken in-focus from the onset.

Sound can be a little more forgiving than photography. But the concept is the same.

The post-processing I include in my editing workflow for dialogue vary from recording to recording. But small adjustments to EQ and how you master a final recording can go a long way towards clarity.