Adverbs should come as near as possible to the verbs they qualify. This is because the meaning of a sentence can change with the change in the position of the adverb.

Compare:

Only he lent me five cents. (= He and nobody else lent me five cents.)
He only lent me five cents. (= He only lent me the money, he didn’t do anything else.)
He lent me only five cents. (= He didn’t lend me more than five cents.)
He lent only me five cents. (i.e. to nobody else)

You will have noticed that the meaning of the sentence changes considerably with the change in the position of the adverb only.

Most adverbs, however, can be placed in different positions with no significant change in meaning. There are, nevertheless, some rules regarding the position of adverbs.

Rule 1

When the verb is intransitive (verbs that do not have objects), place the adverb immediately after it.

He walked slowly.
She smiled beautifully.
He spoke fluently.
He arrived late.
They worked hard.

Rule 2

When the verb is transitive with an object following, place the adverb immediately after the object.

She endured the pain bravely.
He offered his help willingly.
She sang the song beautifully.
He drove the car fast.
He did the job well.
He gave his consent immediately.
He took the matter lightly.

Rule 3

Adverbs of Time and Frequency normally come before the verb. Examples are: always, before, often, never, seldom etc.

They seldom visit us.
She never admitted her fault.
(You) always speak the truth.
He is usually late for office.
It is never too late to mend.

Rule 4

Note that when the verb consists of an auxiliary, the adverb goes after it.

They have never invited us to their parties.
I have always wanted to be a writer.
He was greatly praised for his novel idea.
I have not had the time to look into the matter.
We must always obey our parents.
He is still working at the sum.

Rule 5

An adverb which modifies an adjective or another adverb comes before it.

She is very beautiful. (Here the adverb very modifies the adjective beautiful.)
They are highly competitive. (Here the adverb highly modifies the adjective competitive.)
The girl sang so sweetly. (Here the adverb so modifies the adverb sweetly.)

Note that the adverb enough comes after the adjective it modifies.

He was foolish enough to trust her.
She is old enough to do things on her own.
Our army is strong enough to defend our country.

Rule 6

The words only, merely, even, not and never are usually placed before the words they modify.

I merely wanted to know his name.
She was not clever enough to see through his scheme.
He never keeps his word.