1. Strike whilst the Irons hot. 

Meaning act quickly whilst you are in a good position so you don't miss this opportunity to get in before anyone else. (Before the iron cools down!)

2. Over the moon!

 Meaning I am overjoyed, I could almost jump over the moon.

3. Don't jump out of the frying pan in to the fire. 

Meaning It might be wise to stay where you are, in your current position, as doing something rashly might put you in an even worse position.

4. Out of sight, out of mind. 

Meaning if you can't see something, then you can easily forget about it. (Which may not be a good thing.)

5. Red sky in the evening, shepherd's delight. Red sky in the morning, shepherd's warning. 

When the sky is red in the evening, it's a sign of a good day tomorrow. However, a red sky in the morning means rain, a bad day ahead.