Reading the local newspapers is a great way to improve your Spanish. If your are interested in learning pachuco (local slang), some good Costa Rican expressions (tiquismos) or just understanding the local culture then I recommend you read the la Teja or La Extra.

Here are some words and expressions I found while reading the newspapers:

Bombazo – a car crash. Choque is also used.
Cole – short for high school. Colegio is the correct word. Liceo is a synonym
Cumple – short for birthday. Comes form the word cumpleaños
Echar la casa por la ventana – to spare no expense like when you have a big party or celebration.
Echarse a alguien – to kill somebody
Estar de manteles largos – to put on a party or celebrate an event like a birthday
El poli – slang for police. Policía is the correct word. Tombo or paco are the pachuco words for police.
Hacer trompas – to make faces.
Jalar – means to go in Costa Rican slang. It can also means “to go” when someone dies. For example, María jaló or María se fue mean Maria passes away.
El Monse – short for Hospital Monseñor Sanabria in Punta Arenas.
La pelona – death or the angel of death.
Quesos – packs (pacas) of cocaine taken form smugglers. In proper Spanish queso means cheese.
El reloj – literally means watch or clock but is slang for heart or “ticker.”
Socollón or meneón – a big shaking movement. Another way to say earthquake (terremoto) in the local lingo.