Direct commands use the imperative (mitte, considera, memento), the passive or deponent imperative in -re (distrahere), and, for "do not", ne with the perfect subjunctive (ne siveris).
"Do not": ne + perfect subjunctive (ne siveris "do not allow"), or noli, nolite + infinitive (noli timere "do not be afraid"). nec or neque before an imperative means "and do not".
A 2nd-person present subjunctive can also give an order, more gently: contemnas "despise" (see the jussive subjunctive).