Determination of Lewis Dot structures and visualization of the shapes of molecules using VSEPR theory is an example of an abstract concept that students often find difficult to learn. I have found it useful to have a single worksheet/packet that my students can add to as we cover Lewis dot structures, resonance, VSEPR shapes, polarity, and intermolecular forces.
During our review since last week, resonance was labeled as one of the most tricky concepts (along with electron pushing in my opinion), despite lots of practice and instruction. My teaching sequence consists of defining and providing examples of conjugation (after learning about hybridization), delocalized electrons, and finally pushing electrons if conjugation exists. I remember from teaching at the college level that resonance was also a tricky topic for many undergraduates.