What are some common mistakes students make with Lewis structures?
From a high school student's perspective, the first mistake I made often made was miscounting the valence elections for the compound. Thus, making my bonds, double bonds, triple bonds drawn incorrectly. Also, I didn't know where to place the hydrogens, nitrogens (etc.) around the central atom, I was told it is drawn around the central atom but sometimes I didn't have 4 hydrogens around one carbon atom for say. I also struggled with where to place the dipoles, however now I know you put it towards the more electronegative element....
Basically those were the mistakes I made...basically everything. But if I say so myself I think i've improved since.