Hola Meghan,

The negative commands (negative imperative) for all subjects (tú, vosotros, usted, ustedes, nosotros) will take the form of their present subjunctive, that's why this command: "¡No leamos hoy!" (Let's not read today!) is in the subjunctive form. These two lessons will help you with this: 

Forming the Spanish imperative of tú/ vosotros/vosotras (negative commands)

Forming the imperative for usted/ustedes/nosotros/nosotras (affirmative and negative commands)

I hope this helps.

Inma