Some Important Idioms:

Cross that bridge when you come to it
To deal with a problem or situation when such a problem or situation actually arises.

Curiosity killed the cat
Sometimes, curiosity, that is the thirst to know what one shouldn’t know – can land you in trouble!

Cut corners
Anything not up to the mark in quality because cost saving was the main motive. ‘The dining table had one leg balanced on a piece of wood, because dad was cutting corners!’

Donkey’s years
Doing something for many years without any considerable progress.
Don't count your chickens before the eggs have hatched
Basically means not to be too optimistic! i.e., not to take decisions or make plans without a considerable certainty of the future.

Don't put all your eggs in one basket
Because if the basket falls then all the eggs will get destroyed! As in, don’t keep all your life’s plans or any other plans/ decisions geared to one thing – keep them varied – so lesser chance of total failure!

Drastic times call for drastic measures
Like when the Pandavas had had enough – they went to war! Thus, in extreme cases – one needs extreme measures to counter a situation.

Every cloud has a silver lining
It basically means – be optimistic in the pace of adversity – even though things are dark and gloomy now – the clouds will shift some day or another!