Learn the fundamental laws that govern lightweight designs. You will get insights from how it is done in nature. Also, you will learn the main categories of topology optimization and when to use them.
Learn the classical and modern techniques to create light-weight structures. Trusses are relevant for large scale structures and regular machine parts.
Learn how to do topology optimization by hand. Yes, pen and paper! Use simple geometry to create lightweight topology. This method is very useful during the concept stage of development, and will give you an intuitive understanding of topology.
The fundamental shape for transferring moments.
Buckling is usually not considered in commercial software for topology optimization, but it is crucial to real world practical designs. Learn how to design with buckling in mind.
Don't let fatigue become an afterthought. There is a lot you can do in the design process to increase the life cycle of your part. Learn how to round corners and poke holes in things without creating stress concentrations.