Lo, La or Le?

Ask yourself: does the action fall directly on the person or thing, or does something go to a person?

• Direct object (see, visit, call, invite, buy, put): lo, la, los, las, which show gender and number. La visito (I visit her). Los invito (I invite them).
• Indirect object (the person you tell, give, write, send or show something to): le for one person and les for several, for men and women alike. Le digo la verdad (I tell him/her the truth).

A quick test: if the sentence already has another object (a book, flowers, everything), the person is indirect: Le regalo un libro (I give her a book). The indirect pronoun is often doubled with a + person: ¿Qué le dijiste a Carlos? In Spain, le is also accepted instead of lo for one male person: Le vi = Lo vi.