One of the best classes you can take is Tony Vincent's Classy Graphics course. It's open a few times a year so you'll have to check his site (or Twitter) for the next cohort. Also check out his website for advice on Getting Creative with Google Drawings.
The Power of Google Drawings to Engage Students - https://rechargelearning.blogspot.com/2019/09/the-power-of-google-drawings-to-engage.html
10 Ways to Use Google Drawings in the Classroom - https://shakeuplearning.com/blog/10-ways-to-use-google-drawings-in-the-classroom/
Earn a Black Belt in Google Drawings: (A drawing challenge): https://docs.google.com/document/d/1g_mNqyXDVsg_SByZJdpfKmyhzyFYO4-LOyoFcLPaG3k/edit
Eric Curts shares 30 Free Google Drawing Graphic Organizers using Google Drawing on his Control Alt Achieve blog.
Matt Miller also shares 25 Free Google Drawings Graphic Organizers as well as advice on making your own.
An alternative to using Google Drawings is the use AutoDraw.com. This amazing app can (usually) recognize what you are trying to draw and create a better image for you. Check out Paula's post on how to do this at https://slidesmania.com/how-to-create-icons-for-your-google-slides-using-autodraw/ Eric Curts also has some info on it at https://www.controlaltachieve.com/2017/04/google-autodraw.html
Google Drawings Meme Generator and more templates: https://rechargelearning.blogspot.com/2020/02/google-drawings-meme-generator-and-more.html
Google Drawing Tutorial
Google Drawings Demo
Custom Google Classroom Banner using Google Drawings