Alphabetical list of useful common idioms:
Abandon ship (leave a failing enterprise).
Above and beyond (more than is required).
Aboveboard (in the open, visible to the public, honest).
Ace in the hole (something important held in reserve).
Achilles' heel (weak point or fault in someone or something otherwise perfect).
Across the board ([distributed] equally for everyone or everything).
Add insult to injury (to make a bad situation even worse).
After the fact (after something has happened or taken place).
Ahead of schedule (having done something before the expected time).
All over the place (everywhere, or widely variant, of uneven distribution).
Along those lines (similarly, in nearly the same way).
Around the clock (continuously for 24 hours at a time).
As luck would have it (by good or bad luck, as it turned out, by chance).
Asleep at the wheel (not attending to one's job).
At any rate (in any case, anyway).
At a crossroads (the point at which a decision must be made).
At cross-purposes (with opposing viewpoints, goals that interfere with each other).
At the eleventh hour (at the last possible moment).
At the end of one's rope (at the limit's of one's endurance or patience).
At the helm (in the position of control).
At each other's throats (arguing).
At a dead end (unable to proceed).
At this stage/of the game (currently).
At wit's end (at the limits of one's mental resources).
Breathe easy (relax and recover after something stressful).