Sayings  are quite common in spoken English. We don't normally put them in a composition or a letter. Sometimes it is helpful if you know what common proverbs mean. Here are a few examples. " Once bitten, twice shy." If a dog bites me, I shall be twice as careful in future when I see it. This proverb is also used to apply to many things and not only to dogs. For example, if you have been cheated at a shop, you will not go to the same shop again. "A bird in the hand is worth two in the bush." If I am a hunter, trying to catch birds, it is better to catch one than to see two birds in a bush but not able to catch them. Thus this means that what you have already got is better than the chance of being able to get something bigger in future. " Don't be a dog in a manger " means " Don't be selfish." In a stable  ,the manger is the place where the horse's food is put. Sometimes a dog will sleep in the manger and bark when a horse comes to get its food. The dog doesn't want to eat the horse's food in the manger but it will not let the horse eat it. " He who pays the piper calls the tune  ." A piper is a musician. The man who pays a musician can say what tunes the man will play. Thus this means that if a man provides the money for a plan, he can say how it will be carried out. "To pour oil on troubled waters" is to try to calm things down. Oil is lighter than water. If a ship is in trouble at sea, another ship may come to help it. The second ship can send small boats to rescue people. However, it may first pour oil on the sea to make the sea less rough. Mrs Lin wanted to buy a new dress. Her husband suggested that she buy it from a shop near their home. Mrs Lin disagreed because she had been cheated by that shop. So she said, " I won't go there again because   _   ."
a bird in the hand is worth two in the bush he who pays the piper calls the tune once bitten, twice shy I don't want to be a dog in a manger