Modifiers are descriptive words, phrases, or clauses that modify another word or word group.

Adjectives modify nouns or pronouns and are always singular:
Tracy is wearing a dress. (Unmodified noun)
Tracy is wearing a beautiful, flowing, forest green dress. (Modified noun)

Adverbs modify verbs, adjectives, or other adverbs. When adverbs modify verbs, they generally answer the question when? where? how? why? :
He was walking swiftly.

Adverbs (such as actually, firstly, lastly, finally) can also modify entire sentences:
Finally, they finished their project.

Prepositional phrases function as adjectives or adverbs to modify another word in the sentence:
He was walking towards the door.
She sat on the chair beside the window.

Limiting modifiers - only, even, almost, nearly, just - should be placed in front of the word they modify. Don't place them in front of the verb unless they modify the verb:

Wrong:	You will only need to plant one packet of seeds.
Right:	You will need to plant only one packet of seeds.

Misplaced modifiers are ambiguous phrases and clauses that give a false impression of the meaning of the sentence:

Wrong:	He went back to the house where he was born in a red cadillac dressed in a blue suit.
Right:	Dressed in a blue suit, driving a red cadillac, he went back to the house where he was born.

Dangling modifiers should be avoided. A dangling modifier is usually an introductory word group that suggests but does not name an actor:
Upon seeing the man on the tracks, the train came to a stop.

To repair a dangling modifier, either:

. . . change the subject of the sentence so that it names the implied actor: Upon seeing the man on the tracks, the conductor brought the train to a halt.

. . . turn the modifier into a word group that includes the actor: When the conductor saw the man on the tracks, she brought the train to a halt.

Beware redundant modifiers:

Wrong:	She still hasn't finished her homework yet.
Right:	She still hasn't finished her homework. ~or~ She hasn't finished her homework yet.