I took drafting class in high school. Then during my last year in college in our Residential Landscape Design class we went through further training on how to draw scaled design plans. It wasn't super extensive but my professor at the time (
Dr. Bill Barrick) is now the Executive Director of Bellingrath Gardens in Alabama.) and he know his stuff and I still have all the drawings from that class complete with his hand written notations on them. I was never really good at lettering though. Just never got the knack of it. Here's a very rough design plan I did for a client about 10 years ago. I have done many many sketches and drawings but I prefer to do the actual work itself instead of the drafting part.
I never looked into CAD because I don't specialize in doing plans as much as just doing the work itself. One day when I slow up doing the actual work, I may look into it.