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
