Where an adverb sits in a sentence determines what it modifies and, consequently, what the sentence means. "Only she told him the truth" (no one else told him) differs sharply from "She told him only the truth" (she told nothing but truth). Adverbs of frequency (always, never, often) typically go before the main verb but after auxiliary verbs. Limiting adverbs (only, nearly, almost, just) should be placed directly before the word they modify. Moving an adverb even one position can shift emphasis, introduce ambiguity, or change meaning entirely.
Take a single adverb and move it to every possible position in a sentence, writing out each version and noting how the meaning changes. Then identify the version where the adverb unambiguously modifies its intended target.
You already know that adverbs modify verbs, adjectives, or other adverbs — but placement determines *which* element they actually modify, and moving an adverb even one word can produce a completely different sentence. The technical term for this is scope: an adverb takes scope over the element it immediately precedes (or, in some cases, follows). Position is meaning.
The clearest demonstration is with limiting adverbs — words like *only*, *nearly*, *just*, *almost*, and *even*. Compare: "Only I told him the truth" (no one else did), "I only told him the truth" (I did nothing else to him), and "I told him only the truth" (I withheld nothing). Same words, three distinct claims. In speech, intonation covers up misplacement; in writing, you have only word order. The rule is mechanical: place the limiting adverb directly before the word or phrase it restricts.
Adverbs of frequency (always, never, often, usually, sometimes) follow a different positional rule: they go *before* the main verb but *after* an auxiliary verb. "She always runs" but "She has always run." This pattern is consistent enough to memorize as a positional formula. The logic is that frequency modifies the habitual nature of the main action, so it attaches as close to the main verb as the auxiliary structure allows.
Sentence adverbs (unfortunately, clearly, frankly, obviously) are a third category that can open an entire clause. When you write "Clearly, she understood the problem," *clearly* scopes over the whole proposition — it comments on the obviousness of the entire claim. This is grammatically legitimate and stylistically powerful for signaling your attitude toward a statement. But be careful not to let sentence adverbs drift mid-clause where they can attach ambiguously to a specific verb rather than the whole sentence.
The unifying principle is intentionality: every adverb you place is making a claim about what it modifies. Before finalizing any sentence with an adverb, ask: what is this word actually attached to, and is that the attachment I intend? If moving the adverb one position left or right would change the meaning, you have found the only correct placement — put it there.