expression
first and foremost; above all; most importantly
A set phrase used to emphasize that something is the most important priority or consideration.
何よりもまず、健康が一番大切です。
First and foremost, health is the most important thing.
何よりもまず、安全を確保しなければならない。
Above all, we must ensure safety.
とにかく means 'anyway' or 'in any case', often used to move past details, while 何よりもまず specifically ranks something as the top priority.
まず第一に also means 'first of all', but is more neutral and sequential; 何よりもまず carries a stronger sense of overriding importance.
A fixed phrase composed of 何より (more than anything) + も (emphatic) + まず (first of all).