to keep up: to prevent from sleeping; to continue maintaining (speed, level of work, condition, etc.) Examples of TO KEEP UP If we can keep up this speed, we should arrive there in about three hours. That student has been getting all As. I hope he can keep it up.

few and far between: not frequent, unusual, rare Examples of FEW AND FAR BETWEEN It’s hard to find a trustworthy lawyer; they’re few and far between. Friendships like ours are few and far between, my best friend told me.  

to knock one self out: to work very hard (sometimes too hard) to do somethingA reflexive pronoun must divide the idiom. Examples of TO KNOCK ONE SELF OUT She really knocked herself out trying to pass that difficult class. Don’t knock yourself out during practice. Save your strength for the competition later.

for good: permanently, forever Examples of FOR GOOD “I’m ending this conversation for good!” she yelled, storming out and slamming the door. It feels great to have the race finished for good.

to make friends: to become friendly with others Examples of MAKE FRIENDS Once you’re done with college, it’s hard to make friends, but it isn’t impossible. The kittens approached each other tentatively, hoping to make friends.  

to call for: to require; to request, to urge Examples of TO CALL FOR The insult wasn’t even mean enough to call for a response. A question calls for an answer.