A Bird In The Hand Is Worth Two In The Bush: 
Having something that is certain is much better than taking a risk for more, because chances are you might lose everything.

A Blessing In Disguise: 
Something good that isn't recognized at first. 

A Chip On Your Shoulder: 
Being upset for something that happened in the past. 

A Dime A Dozen: 
Anything that is common and easy to get.

A Doubting Thomas: 
A skeptic who needs physical or personal evidence in order to believe something.

A Drop in the Bucket: 
A very small part of something big or whole.

A Fool And His Money Are Easily Parted: 
It's easy for a foolish person to lose his/her money. 

A House Divided Against Itself Cannot Stand: 
Everyone involved must unify and function together or it will not work out. 

A Leopard Can't Change His Spots: 
You cannot change who you are.

A Penny Saved Is A Penny Earned: 
By not spending money, you are saving money (little by little).

A Picture Paints a Thousand Words: 
A visual presentation is far more descriptive than words.

A Piece of Cake: 
A task that can be accomplished very easily.

A Slap on the Wrist: 
A very mild punishment.

A Taste Of Your Own Medicine: 
When you are mistreated the same way you mistreat others.

A Toss-Up: 
A result that is still unclear and can go either way.

Actions Speak Louder Than Words: 
It's better to actually do something than just talk about it.

Add Fuel To The Fire: 
Whenever something is done to make a bad situation even worse than it is.

Against The Clock: 
Rushed and short on time.

All Bark And No Bite: 
When someone is threatening and/or aggressive but not willing to engage in a fight.

All Greek to me: 
Meaningless and incomprehensible like someone who cannot read, speak, or understand any of the Greek language would be.

All In The Same Boat: 
When everyone is facing the same challenges.

An Arm And A Leg: 
Very expensive. A large amount of money.

An Axe To Grind: 
To have a dispute with someone.

Apple of My Eye: 
Someone who is cherished above all others.

As High As A Kite: 
Anything that is high up in the sky.

At The Drop Of A Hat: 
Willing to do something immediately.