She's a useful person to know.
John is a useful person to be around on such occasions.
Horses are useful animals.
I need a useful dictionary.
He gave us some useful advice.
Salt is a useful substance.
This is a useful book for beginners in English.
The England cricket team scored quite a useful total.
Money is always useful.
Information about people's language ability is often very useful.
S+be+～+ prep .-phrase
He is useful at cooking.
He is very useful at maths.
These books might be useful to you.
These story books are useful to children.
Your advice was very useful to me.
We should absorb whatever experience is useful to us.
Tom's advice has been most useful to us.
Such information is useful only to those who know that particular subject.
Outdoor sports are useful to your health.
This book will come in useful for criticizing the wrong behaviour.
The computer is useful in processing data.
It is/was+～+(for sb+) to- v
It is useful to read the text early in the morning.
It is very useful for a person to know how to swim.
Probably it will be useful for them to acquire a practical knowledge of English.
It is/was+～+ v -ing
It's useful knowing several foreign languages when you are traveling abroad.
I find this pen very useful.