Negative Informal (tú) Commands in Spanish

Unlike affirmative informal (tú) commands that use the 3rd person singular form of the present indicative, negative informal (tú) commands use the tú form of the present subjunctive of each verb. Alternatively, if you're familiar with formal commands, you can also form the negative informal command by simply adding an -s to the end of the negative formal (singular) command. Consider the following examples.
Negative Formal (Ud.) Command
Negative Informal (tú) Command
No compre el maquillaje.
(Don't buy the makeup.)
No compres el maquillaje.
(Don't buy the makeup.)
No coma ese pan.
(Don't eat that bread.)
No comas ese pan.
(Don't eat that bread.)
ˇNo escriba la carta!
(Don't write the letter.)
ˇNo escribas la carta!
(Don't write the letter.)

Pronoun Placement with Negative Informal Tú Commands

When a pronoun is used in conjunction with a negative informal (tú) command, it is placed before the verb in the negative command, but after the negative word (ie. "no", etc.) Read and listen to the following examples, then repeat each out loud.

Don't sit down at the table before you wash your hands.
No te sientas en la mesa antes de lavarte las manos.
Never give money to the boys.
Nunca les des dinero a los chicos.
Never give it to them.
Nunca se los des.

Irregular Negative Informal Tú Commands

In Spanish, there aren't any irregular negative informal commands. Those verbs that are irregular in the present subjunctive maintain their irregular form in the negative tú command. Read and listen to the following examples, then repeat each out loud.

Tell the truth.
(Affirmative "tú" command)
Di la verdad
Do not tell lies.
(Negative "tú" command)
No digas mentiras.
Do your work.
(Affirmative "tú" command)
Haz tu trabajo.
Don't do your work.
(Negative "tú" command)
No hagas tu trabajo.