¡No llores! ("Don't cry!") is a useful command to know -- especially if you're the parent of a small child or a serial heartbreaker. It's also the title of a featured song by singer Gloria Estefan.
Did you know that negative, informal commands are formed differently than affirmative ones? You see, once you add a no, informal commands require the tú form of the present subjunctive to be grammatically correct. That means an -ar verb like llorar ("to cry") takes the second-person subjunctive ending -es to become no llores as a negative command.
To help you learn this grammar rule through repetition, just listen to the opening of this song:
No llores, no llores, no llores, no llores...
Don't cry, don't cry, don't cry, don't cry...
Caption 1, Gloria Estefan - No LloresPlay Caption
Got that? If the singer wanted tears to fall, she might have ordered, "llora, llora, llora, llora..." ("cry, cry, cry, cry...").
Now let's look at a line of the song with a little more vocal variety:
No te preocupes, deja el llanto y escucha mi canto que dice así...
Don't worry, leave your crying and listen to my singing that goes like this...
Caption 29, Gloria Estefan - No LloresPlay Caption
In this one line, we have three -ar verbs -- preocupar(se), dejar and escuchar -- in command forms. Did you notice that no te preocupes ("don't worry") takes the -es ending while the two positive commands -- deja ("stop") and escucha ("listen") -- simply end with "-a"? In the affirmative, informal commands tend to look like the third-person indicative, with some exceptions, for example:
Decir as a command is "di" -- as heard in caption 15 of this same song -- and hacer is "haz" -- as heard in caption 6. You can review informal command forms here, and/or here.
Note that the verb "dejar" can mean "to leave, to quit, to cease, to stop." So, "¡Déjame en paz!" means "Leave me alone!" (or, more literally, "Leave me in peace!"). "Dejar de" + an infinitive means "to stop [doing something]." Here's part of the song that illustrates:
No llores... -Deja de llorar, deja de llorar, deja de llorar
Don't cry... -Stop crying, stop crying, stop crying
Caption 10, Gloria Estefan - No LloresPlay Caption
Deja de sufrir y suelta los temores
Stop suffering and let go of the fears
Caption 12, Gloria Estefan - No LloresPlay Caption