A cada puerco le llega su sábado / San Martín.
Everyone gets his comeuppance in the end / just deserts sooner or later.

 A diario una manzana es cosa sana.
An apple a day keeps the doctor away.

 A donde el corazón se inclina, el pie camina.
Home is where the heart is.

 A donde te quieren mucho no vengas a menudo.
A constant guest is never welcome.

A falta de pan, buenas son (las) tortas / las tortas son buenas.
We’ll just have to make do.

A la ocasión la pintan calva.
You have to make the most of the chances that come your way.
You have to strike while the iron is hot.

A los tontos no les dura el dinero.
A cool and his money are soon parted.

 A más honor, más dolor.
The more danger, the more honor.

 A palabras necias, oídos sordos.
Take no notice of the stupid things people say.

A quien no le sobra pan, no crie can.
Never spend your money before you have it.