Build the prohibition first, then complete the sentence naturally.
لَا تَخَفْ إِنَّ اللَّهَ مَعَنَا — do not fear; surely Allah is with us.
لَا تَدْخُلُوا مِنْ بَابٍ وَاحِدٍ — do not enter through a single gate.
لَا تَكْتُمُوا الشَّهَادَةَ — do not conceal testimony.
Notice: singular تَخَافُ becomes تَخَفْ when jussive; this weak-verb change is shown here as a complete form to recognize, not generalized into a new weak-verb lesson.