to take hold of

to take hold of: to grasp, to grip with the hands

• You should take hold of the railing as you go down those steep stairs.
• The blind man took hold of my arm as I led him across the street.

to look into

to look into: to investigate, to examine carefully (also: to check into)

• The police are looking into the matter of the stolen computers.
• The congressional committee will check into the financial dealings of the government contractor.

to do over

to do over: to revise, to do again(S)

A noun or pronoun must separate the two parts of this idiom.

• You'd better do the letter over because it is written so poorly.
• Jose made so many mistakes in his homework that the teacher made him do it over.

ill at ease

ill at ease: uncomfortable or worried in a situation

• Speaking in front of a large audience makes many people fell ill at ease.
• My wife and I were ill at ease because our daughter was late coming home from a date.

to be up to

to be up to: to be dependent on the decision of another; to be doing as a regular activity; to feel able to do something

The second definition is most often used in a question as a form of greeting.

• I don't care whether we go to the reception or not. It's up to you.
• Hi, Evan. I haven't seen you in a while. What have you been up to?
• Alexi isn't up to going on a hike; his broken foot is still holding.

to find fault with

to find fault with: to criticize, to complain about something

• It is very easy to find fault with the work of others, but more difficult to accept criticism of one's own work.
• Mrs.Johnson is always finding fault with her children, though they really try to please her.

to keep away (from) / stay away from

to keep away (from): to stay at a distance (from)(s); to avoid use of (also: stay away from)

• Please be sure to keep the children away from the street!
• The signs on the burned-out house said, "Keep Away! Danger Zone."
• It's important to stay away from dangerous drugs.

to keep out

to keep out: not to enter, not allow to enter (S)

• There was a large sign outside the door that said, "Danger! Keep out!"
• I've told you to keep the dog out of the house.

by heart

by heart: by memorizing

• He knows many passages from Shakespeare by heart.
• Do you know all the idioms you have studied in this book by heart?

to make an impression / to leave an impression

to make an impression: to influence another person's opinion of oneself (also: to leave an impression) (S) 

This idiom is usually separated by an adjective such as good or bad.

• Abigail made a good impression during her job interview, so they offered her the position.
• With his awful manners and personality, Karsten leaves a bad impression on everyone he meets.