Usage patterns
〈人〉を大切にするto treasure/cherish someone
He treasures his family very much.
〈物〉を大切にするto take good care of something
I take good care of the watch my grandmother gave me.
〈事〉が大切だsomething is important
Maintaining good health is important.
〈人〉にとって大切な〈物〉something precious/important to someone
This is a precious memory to me.
Expressions
大切にするcherish; treasure; prize · take good care of; look after