Idioms are speech forms that follow no easily specified rules. The English say “Maria went to hospital,” an idiom strange to American ears, which are accustomed to hearing the in front of hospital. Native speakers of a language seldom have problems with idioms, but prepositions sometimes cause trouble, especially when they follow certain verbs and adjectives. When in doubt, consult a good desk dictionary: Look up the word preceding the troublesome preposition.
Idiomatic usage
ESL: Idioms
Exercise: Standard idioms 1
Exercise: Standard idioms 2