“The calm before the storm”

“A mixed bag”

A combination of good and bad things.

“A double-edged sword”

Something that has both advantages and disadvantages.

“Big picture”

The overall situation, not small details.

“Break new ground”

To do something innovative or original.

“Not my cup of tea”

Not something one likes or enjoys.

“Brush up on”

To improve knowledge or skill in something.

“Brace yourself”

Prepare yourself for something difficult or unpleasant.

“Hit a wall”

To reach a point where no further progress seems possible.