A modifier is a word, phrase, or clause that describes, clarifies, or gives more details about nouns or verbs in a sentence.
He earned almost a thousand bucks for the show.
A misplaced modifier is when the modifier is NOT placed next to the word it modifies.
He almost earned a thousand bucks for the show. (=actually he did not earn anything.)
Fixing misplaced modifiers is simple. (1). identify the modifier, (2). identify the word(s) being modified, and (3). move the modifier next to the words being modified.
In the example given above,
a thousand bucks=words being modified
He earned almost a thousand bucks for the show=moving modifier next to the words being modified.
prepositional-phrase modifiers, relative-clause modifiers, limiters or participle-modifiers are commonly misplaced. See the powerpoint below to know more about misplaced modifiers: