何: accent on first syllable
何(something the speaker doesn't want to say directly): flat
何かある: accent on first syllable
何もない: flat
何も(an adverb as in 何もそんなに怒らなくても): accent on first syllable
誰: accent on first syllable
誰かいる: accent on first syllable
誰もいない: flat
誰もが驚いた: accent on first syllable
But I'm still kind of confused in exactly what kind of situation should I use a flat tone? When you are not trying to sound assertive?
Also, does this apply to other words besides 誰 and 何?
The flat-type accent is applied to total negation. When used in set phrases such like the ones in the following examples or with particles other than も, flat (=0) and accent on first syllable (= 1) are both possible even for total negation. どこ and どう have the same accent pattern, too.