With a bit of practice, you can easily create Lewis structures for almost any molecule. Use the following procedure as a guide to creating Lewis structures.
Let's consider nitromethane shown below. This is the Lewis structure we are attempting to create. The condensed structure is shown on the left and your goal is to generate the Lewis structure on the right.
For negative charges add the corresponding number of electrons, for positive charged atoms subtract electrons.
In the case of nitromethane, since the molecule is neutral we do not need to adjust.