。
Try to make good use of your free time.
Literal
Free-time [object-を] skillfully use-[in-order-to-ように] endeavor-[soft-imperative-なさい].
A textbook-style piece of advice. うまく is the adverbial form of うまい ('skillful, adept'); here it means 'skillfully, effectively.' The chain ~ように努める ('endeavor so as to') is a polite, slightly bookish way to frame an aspiration: literally 'make it your effort to use your free time skillfully.'