el burro delante, para que no se espante

Etymology
lit. 'the donkey at the front, so it doesn't get scared'.

Usage notes

 * The phrase is used as a reminder that in sentences such as "Yo y Pablo vamos a Madrid" (Me and Pablo are going to Madrid), it is polite to change the order of the subjects of the sentence by putting "yo" (I) after the other subjects. The more proper sentence in this example would read "Pablo y yo vamos a Madrid" (Pablo and I are going to Madrid).
 * The phrase is often shortened to el burro por delante.