As often happens with many verb groups or pairs, the difficulty in usage is often due to there being one verb in English that is used in more than one sense. Learn how this can often be avoided by remembering two different translations of these two verbs.
How These Two Verbs Differ
The main differences between the two verbs salir and dejar are best demonstrated by translating their most frequent translations into English, beginning with when they are employed as stand-alone verbs (that is, when dejar is not used as an auxiliary verb).
Salir almost always means to exit. When speaking of how things turn out (test results, for instance) then, it means, to turn out or to result in. In the preterite, salir also corresponds to the English expression using the verb to go -- how something went. In this respect, the Spanish verb ir (in the preterite, usually, but not exclusively) can also be used.
Let's examine a few sentences with salir in these senses:
1. Juan sale para Veracruz en dos días. (John is leaving for Veracruz in two days.) Note how the idea of exiting is involved, even if that verb is not used in English?
2. ¿Qué tal te fue el examen? (How'd the test go for you?) Note how the idea of things turning out well or badly is involved in this use of salir, in the preterite?
3. Siempre salía mal de los exámenes hasta que me enseñaste el uso de salir. (I always did badly on tests until you taught me the use of salir.) Note how the imperfect of salir still carries the same idea as it does when used in the preterite, in this context -- this time, with the sense of things going well or badly in the past.
Salir, used with con, is the way one expresses the concept of going out with someone, including, but not limited to the English verb to date:
1. Juan sale con Teresa ahora. (John is dating Teresa nowadays.)
2. Los jefes salen con los ejecutivos para tomar los viernes. (The bosses go drinking with the CEOs on Fridays.)
The verb dejar is somewhat more nuanced because it can be used as an auxiliary verb in two different ways, with two different meanings. When used alone, it translates as to leave [something or someone] behind. When used in the sense of leaving someone behind, it is often in the sense of to abandon or to stand up.
In this lesson, I'll only deal with dejar as a stand-alone verb, to establish the fundamental distinction between these two verbs. Used with an indirect object pronoun, the verb dejar can mean to bequeath or leave for someone (it need not be something good, since someone could leave you holding the bag, so to speak).
1. Voy a dejar mi billetera en casa. (I'm going to leave my wallet at home.) Note that here, the verb dejar means to leave something behind.
2. Juan la dejó por otra mujer. (John left her for another woman.) Note that here, the verb dejar means to abandon or to stand up (as in to jilt).
3. Mi abuelo me dejó diez mil pesos cuando falleció. (My grandfather left me ten thousand pesos when he passed away.) Note that here, the verb dejar means to bequeath, as in a last will and testament.
These meanings of salir and dejar, when used as stand-alone verbs, apply in all tenses and moods.