International Students taking A-level

how exactly does A-level work in the admissions committee? i mean, how many A-level subjects or credits does the admissions want to see in their applicants? are 3 A level and 2 AS level subjects enough to get into a good college or simply not rigorous enough? and what kind of subject choices do they prefer? does taking subjects that do not encompass liberal arts, such as taking courses only in sciences, english and math, make a bad combo?