Breath support, resonance and pacing — a few minutes a day, built around what your voice actually does, with the vocal health bits nobody mentions.
Trailing off, going quiet, and much of the shakiness all trace back to shallow chest breathing. Almost everything else improves once that does.
Not volume. Speaking faster is what nerves do, and the instinctive fix — talking louder — makes your throat ache without making you clearer.
Speaking below your natural range strains the voice and produces exactly the gravelly quality people are trying to get rid of.
Hoarseness lasting weeks, pain, or losing your voice repeatedly needs examining rather than exercising through. Voice training products almost never say so.