Whenever you study, always make the fullest use of a dictionary.
Literal
Study-time [topic-は] always maximum [adverbial-に] dictionary [obj-を] utilize-(polite command).
活用する ('to utilize, make full use of') is a noun-する verb — notable because 活用 has another grammar-specific meaning ('conjugation' of verbs/adjectives), so context matters. 最大限に ('to the maximum extent') is an adverbial phrase. The polite imperative ~なさい closes with firm but friendly direction.