Empiricism argues that sense experience is the primary source of knowledge (posteriori).
Rationalism argues that Reason or intellect is the primary source of knowledge (priori).
Empiricists (like Locke, Hume) believe the mind is a blank slate ($tabula$ $rasa$) at birth.
Rationalists (like Descartes, Spinoza) believe in innate ideas present in the mind at birth.
Empiricism relies on the Inductive method (observation to theory), while Rationalism relies on the Deductive method (theory to specific truth).