Draw the lewis structure for nitrogen tribromide

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.