have an early night	go to bed early
grey matter	brains, szare komórki
get a move on	pospiesz się, hurry up
bite off more than you can chew	rzucać się z motyką na księżyc
with a view to doing sth	with the intention/hope of doing sth
with flying colours	with great success
to live on a shoe string	on a very small budget
it's all Greek to me	not easily understood
pull one's socks up	make a greater effort/wziąć się w garść
break the ice	ease the tension when one first meets ppl)