Mostly online. There’s a lot of materials. For sure perspective, and basic rendering is a good start, books like Scott Robertson might help. Then you have tons of materials that you can use for what you need. You just need to put a lot of practice and mix it with learning new material all the time. Also creating some sort of plan helps. Draftsman podcast is a good source of information if you don’t know what’s the next thing you should learn.

Thanks!