"I have been a poor student this year; I need to turn over a new leaf and improve."
An example of an Idiom for Insincerity is: The cat weeping over the mouse [that he has just eaten]. a wolf in sheep's clothing pulling the wool over someone's eyes
This is not an idiom. "It's over" means that it is over, or finished, or done. Whatever "it" refers to has concluded.
The plural of penny is pennies.Some example sentences with "pennies" are:She dropped the pennies all over the floor.He paid for the fare in pennies, much to the driver's annoyance.
Over there.
"Head over heels in love" would be one idiom.
You really have a chip on your shoulder. Don't get a chip on your shoulder over such a little thing.
You don't underestimate
Get back in the saddle.
start from scratch
Imperative sentences give commands. For example: Stand over there. Put your books on the desk. Interrogative sentences ask questions or make requests. For example: May I have a glass of water, please? Are you the new teacher?
Over a Barrel: helpless, at a disadvantage
I don't know what you mean by "common phrases of," but the idiom "over and above" just means "more than what was agreed upon."