Some Important Idioms:

Kill two birds with one stone
To achieve two goals with a single attempt! Like, say, Abhinav Bindra getting an Olympic Gold and a World Record with a single try!
Last straw
The very last problem which usually ends up making people lose their patience.
Let the cat out of the bag
To reveal any information which was asked or considered to be kept a secret.
Make a long story short
To bring out the main points leaving all the unimportant things out.
Method to madness
Although things may seem haphazard and cluttered and confused – but there is actually some method or structure to it. ‘My room may seem untidy and smell of stale pizzas, but there is method to my madness – I find it relaxing to my hyper active nerves!’
Miss the boat
To miss a chance.
Once in a blue moon
To occur very rarely. ‘Once in a blue moon I take my family out for dinner.’
One track mind
To think in only a particular way or manner.
Penny for your thoughts
‘Penny for your thoughts, tell me what you’re thinking.’ It literally means asking someone as to what they are thinking at the moment.