It is important for me to spend time with my family.

You could also say: It is important to spend time with my family.

If you say "It is important..." then the next part would be the infinitive.

E.g. It is important to eat a healthy breakfast.

It is important to exercise regularly.

It is important to wash your hands.

Hello Mimi,

is the correct sentence.

Thank you for your explained Mr. Gary and Miss Juliana

As said by William, to spend is correct.

Note however, you could start a sentence by saying for example: Spending time with my family is what I prefer to do the most at the weekend.

In the gerund here, it denotes an activity.

Thank you Mr. William