When studying a foreign language, sometimes people don’t learn phrases and expressions for speaking colloquially, as people really speak on the street. Become familiar with Spanish sayings and idioms and speak Spanish like a native speaker.

Colloquial language —which includes idioms, sayings and slang phrases— is distinct from formal speech or formal writing. It is the variety of language that speakers typically use when they are relaxed and not especially self-conscious.
Spanish Sayings
The Merriam-Webster Dictionary defines a saying as an “old and well-known phrase that expresses an idea that most people believe is true.” The Macmillan Dictionary also defines it as “a well-known statement about what often happens in life.” For example, “No news is good news” is a saying meaning that if we are waiting for news about someone, it's probably good if we hear nothing because “bad news” would arrive quickly.
Here are some examples of Spanish sayings:
¡Es pan comido! - It's a piece of cake!
Borrón y cuenta nueva - Kiss and make up
De tal palo, tal astilla - Like father, like son
Dejemos las cosas en claro - Let's get things clear
¡Qué pequeño es el mundo! - (It's a) Small world!
Más vale pájaro en mano que ciento volando - A bird in the hand is worth two in the bush
A palabras necias, oídos sordos - A foolish words, deaf ears
En las malas se conoce a los amigos - A friend in need is a friend indeed
Las palabras se las lleva el viento - Actions speak louder than words/voice
Las penas con pan son menos - All griefs with bread are less
No todo lo que brilla es oro - All that glitters is not gold
Tan claro como el agua - It's as clear as day
Más vale tarde que nunca - Better late than never
Más vale prevenir que lamentar - Better safe than sorry
Más vale malo conocido que bueno por conocer - Better the devil you know than the devil you don't
Caiga quien caiga - Come hell or high water
No hay mal que por bien no venga - Every cloud has a silver lining
Cada quién habla como le va en la feria - Everyone sees things from his / her own point of view
Cría fama y échate a dormir - Give a dog a bad name (and hang it)
Haz el bien sin mirar a quién - Do what is right, come what may
El que quiera azul celeste, que le cueste - He that would have the fruit must climb the tree
El que ríe último ríe mejor - He who laughs last, laughs longest
Lo barato sale caro - If you buy cheaply, you pay dearly
En boca cerrada no entran moscas - If you keep your mouth shut, you won't put your foot in it
El que se fue a la Villa perdió su silla - If you leave your place, you lose it
Piensa mal y acertarás - If you think the worst, you won't be far wrong
Es cuestión de vida o muerte - It's a matter of life and death
Está para chuparse los dedos - It's finger licking good
Más vale solo que mal acompañado - It's better to be on your own than with people you don't like
Que sea lo que Dios quiera - It's in the lap of the Gods
Ladrón que roba a ladrón tiene cien años de perdón - It's no crime to steal from a thief
Más se perdió en la guerra - It's not the end of the world
Al que madruga Dios lo ayuda - It's the early bird that catches the worm
Cuentas claras, amistades largas - Let's get things clear
La distancia es el olvido - Long absent, soon forgotten
Ahogarse en un vaso de agua - Make a mountain out of a molehill
No sólo de pan vive el hombre - Man cannot live by bread alone
Dinero llama a dinero - Money goes where money is
No dejes para mañana lo que puedes hacer hoy - Never put off till tomorrow what you can do today
No hay mal que dure cien años - Nothing goes on for ever
Hombre prevenido vale por dos - One good fore wit is worth two after wits