Idioms are an essential part of the Russian language, that can help you with understanding the culture and mentality!

15 Essential Russian idioms used in conversations daily.

To take oneself in one's hands 
/vzyat' s'eb'a v ruki/
To regain one's normal mental state, to regain one's self-control.

To sit in a puddle.
/s'est' v luzhu/
To get oneself into an awkward position or compromising situation.

Neither down nor feathers
/ni pooha ni pira/
Good luck; break a leg
Used to wish someone a successful endeavour, such as a job interview or an exam. The answer would be "К чёрту!", which means ‘to the devil !'

With sleeves pulled down
/spustya rukava/
To do a task carelessly, negligently
Back in the days rich people wore clothing with sleeves so long, making it impossible to do any physical work unless they are rolled up.

The tongue is well-hung
/yazyk harasho padvyeshen/
Eloquent, talkative; in possession of the gift of gab.

As much as the soul wills
/skol’ka dushe ugodna/
As much as you want.

To look through both (eyes)
/smatret’ v obah/
To keep one’s eyes peeled; to be on the lookout.

To build sky castles 
/stroyeet’ vazdushnye zamkee /
To have unrealistic hopes, plans, ideas.

Cтроить воздушные замки

The hands don’t reach it
/rukee ni dahodyat/
 To not find the time to do (something).

By which fates...?
/kakeemee sud’bamee/
How surprising to meet you here.

To leave with the head
/uhadit’ s galvoy v__/
To be fully engrossed/immersed (in something).

Уходить с головой (в ____)

To burn with shame
/sgarat’ at styda/
 To be ashamed.

To look the truth in the eyes
/smatret’ pravdye v glaza/
To face up to something; to face the truth

Cмотреть правде в глаза

To look through one’s fingers
/smatret skvoz’ pal’tsy/
To ignore; to turn a blind eye

Cмотреть сквозь пальцы

Neither heard nor smelt; (no rumors, no smell)
/ni sluhu, ni duhu ot__/
No news from someone; neither seen nor heard