hit the nail on the head	do something properly (trafic w sedno)
keep sth under one's head	hide sth, keep sth in secret
make both ends meet	wiazac koniec z koncem, radzic sobie
blow the whistle	to inform (probably authorities) about sth, zaalarmowac (pozytywne zabarwienie)
break the ice	lamac lody;]
take the bull by the horns	finally decide and take the risk
feather one's nest	make your life comfortable (usually negative meaning) in expence of others - urzadzic sie kosztem ..
burn the midnight oil	learn or work till very late
get into hot water	get in trouble
let the cat out of the bag	reveal a secret
spill the beans	reveal a secret
bark up the wrong tree	accuse wrong person
have a flutter	make a bet
pull one's socks up	start working
buy for a song	buy for a very little money, to have a bargain
hold one's tongue	you might say sth offensive but you don't
bring the house down	give a brilliant performance
put one's foot down	heavily accelerate in your car / be very deceisive
the early bird catches the worm	kto rano wstaje temu pan Bog daje
move the goalpost	unfairl alter the conditions or rules during it's course
steal someone's thunder	to prevent someone from receiving an acclaim for doing sth by doing it or sth similar first
beat about the bush	to discuss sth without coming to the point
level the playing field	situation in which all those involved have an equal chance of being successful
not pull one's punches	to speak in an honest way without trying to be kind
cook the books	to alter records, esp. financial accounts, to conceal irregulatives or wrongdoing
below the belt	unfair or often harmful
pay the lip service	an expression or agreement that is not supported by real conviction
call a spade a spade	speak plainly and frankly
leave someone holding the baby	leave someone responsible for everything