не + verb - the general rule

Не is unstressed and always sits immediately before the verb it negates, never separated from it by another word. Не гледам телевизију. (I don't watch television.) - see present-tense-regular-verbs-a1.

Negative pronouns and adverbs require double negation

Serbian has a full set of negative pronouns and adverbs (see the table below). Whenever one appears in a sentence, the verb still needs its own не (or the fused нисам/нема) - dropping it is wrong even though the sentence already has a negative word.

Нико не зна literally reads "Nobody doesn't know," but means simply "Nobody knows." This double marking is required, not optional, however many negative words the sentence has: Никад никог нигде не видим. (I never see anyone anywhere.) stacks three negatives plus не, and that's entirely normal, correct Serbian.

Special cases

Немати already carries its own negation, so it's never paired with a second не before it - but it still triggers the same double-negation pattern with negative pronouns: Немам ништа. (I have nothing.), not *Имам ништа.

Нема (the impersonal 3rd-person form of немати) also means "there isn't/aren't any": Нема никог код куће. (There is nobody home.)