A drowning man will clutch at a straw	tonący brzytwy...when you are desperate, you will look for anything that might help you
A leopard never changes its spots	one cannot change the basic way one is
when the cat's away the mice will play	when the person in authority is absent, people will not do what they should do
The proof of the pudding is in the eating	real value of sth can be judged only from practical experience not theory
Tell the truth and shame the devil	tell the truth even though you have strong reasons for concealing it
People who live in glass houses shouldn't throw stones	ludzie w szklanych domach nie powinni rzucać kamieniami
Look before you leap	think about sth before u do this
Nothing ventured, nothing gained	if you do not take risks, you will never accomplish anything
One man's meat is another man's poison	Co dla jednego pokarmem, dla innego trucizną
Birds of a feather flock together	similar people tend to associate with each other