Take a foreign language course every year in high school (four consecutive years in one language for fluency)!
Although the high school requirement in most states for foreign language is two years, most colleges prefer to see three consecutive years in one language. In addition to this, by the third year of language study much of the grammar is taught and the fourth year usually focuses on fluency.
There are few skills as helpful in life as fluency in a foreign language – it’s a valuable goal to achieve in high school.