Being unimportant is like being small or light.Being important is like being large or heavy.
I have two little points to make.
I have are some tiny mistakes to correct.
The novel seems very lightweight/thin/slight.
I don't expect you to be impressed:it must seem very small beer/potatoes to you.
I'd rather be a big fish in a little pone than the other way around.
This is a big opportunity for me.
He is the greatest writer of the twentieth century.
It is a sizeable/massive achievement.
These are the weighty matters.
They are the only intellectual heavyweights in the government.