。
You should try to live within your means.
Literal
Within-one's-means living [object-を] do [purpose-ように] should.
~べきだ expresses moral obligation or strong recommendation — 'should.' Stronger than the soft ~たほうがいい ('it would be better to') but softer than ~なければならない ('must'). 分相応 means 'proportionate to one's standing,' rendering the financial advice as a matter of social fitness.