Frequency adverbs tell how often something happens. Examples are: often, never, always, sometimes, generally, usually, seldom, rarely, hardly, ever, frequently etc.

Position of Frequency Adverbs

Frequency adverbs can go in the following positions in a sentence:

Before the principal verb

Structure: subject + adverb + verb + object etc.

He never eats vegetables.
I often buy foreign periodicals.
They frequently visit us.
I always read commercial news.
They rarely watch sports channels.
I sometimes watch English films.

After the verb be

Subject + be + adverb + complement etc.

He is always late for office.
We are never invited to dinner parties.
I am always worried about my finances.
He is sometimes consulted by investors.
You are seldom anxious about my health.

Between the auxiliary and the principal verb

When the verb consists of an auxiliary verb, the frequency adverb goes after it.

He has always done justice to all.
I have often thought of starting a business.
I have never forgotten those unfortunate events.
I have sometimes managed to hoodwink others.
We could hardly ever appreciate his conduct.
We shall never seek such favors.
They will always regret having done this.
They will usually take such big risks.

Notes

Some frequency adverbs (e.g. usually, normally, often, frequently, sometimes and occasionally) can also go in the beginning or end of a sentence.

He writes often.
We visit them frequently.
Sometimes I am late for office.

Always, ever, never, seldom and rarely

The adverbs always, ever, never, seldom and rarely need to be placed before the verb. These adverbs cannot be placed in the beginning or end of a sentence.

Adverbs usually go after the auxiliaries. But when the auxiliaries need to be stressed, they are sometimes put after the adverbs.

I sometimes am worried about my health.
We never should do such things.
You always have done justice to all.

Used to and Have to

Used to and have to are always placed after adverbs.

We sometimes used to stay up the whole night.
He occasionally used to write to me.
The fire brigade always has to be ready to face any emergency.