Wiktionary
apply oneself
vb. (context idiomatic English) To put forth a concerted effort; to try; to focus.
Usage examples of "apply oneself".
When one must apply oneself almost incessantly to the tasks of survival there is little time to indulge oneself in the luxury of conquest.
She had learned what any bond-maid swiftly learns, that one must apply oneself, and be rational, if one will survive on the oar.