Step 1:
Add valence electrons of each element present in molecule,
N = 5
Br = 7
Br = 7
Br = 7
___________
Total 26
Step 2:
Draw Nitrogen in center surrounded by Br atoms and connect them with single bond and subtract 2 electrons/bond from total electrons. As there are three single bonds formed so subtract 6 electrons from total valence electrons.
26
- 6
_______
20
Step 3:
Now start adding these remaining 20 electrons in pair starting from most electronegative element. So, 18 electrons are added to Br atoms and 2 electrons are added to N atom. Now, all the atoms present in the structure have there octet complete.