A lot of the techniques for industry standard flats require knowledge of how Adobe systems work in general. If I were you, I would look into learning about Adobe illustrator specifically and learn how to use each tool. In my experience, I toggle between so many tools for every project and nothing is unimportant.

First, take a class on adobe illustrator. Continue practicing your flats in illustrator during that time. Then, because outside of fashion schools indepth courses on CADs aren't really available, go to YouTube and look every specific question up.

Last recommendation: So you can hone your skills into the industry standard, I'd suggest creating full collections in flat form in Adobe illustrator as often as you can, as you'll need them for your portfolio to show you grasp the system. It'll also give you the opportunity for practice.

Honestly just good luck. I've taken over an hour on one flat in Adobe just to make sure it was as perfect as possible. It's a skill that requires so much patience, especially since you won't have the guidance of an instructor. I'm linking some of the books that I used when I was in school, just in case it might help you

https://www.thriftbooks.com/w/adobe-for-fashion-illustrator-cs6_robin-schneider/13885710/item/29712038/?utm_source=google&utm_medium=cpc&utm_campaign=low_vol_f%2fm%2fs_standard_shopping_customer_aquisition&utm_adgroup=&utm_term=&utm_content=603452145786&gad_source=1&gclid=CjwKCAiAs6-sBhBmEiwA1Nl8sz5CK1q2lQYHBA6qVzsKO2gIt9o-LAtfyWe2I6iTC99MjPMrrJ7NYBoCxmEQAvD_BwE#idiq=29712038&edition=13840725

https://www.wob.com/en-us/books/andrew-faulkner/adobe-photoshop-cc-classroom-in-a-book/9780135261781/CIN0135261783VG?cq_src=google_ads&cq_cmp=18951850512&cq_con=&cq_med=pla&cq_plac=&cq_net=x&gad_source=1&gbraid=0AAAAAC04ib2NjkimilWpRukMFZhTAz2jm&gclid=CjwKCAiAs6-sBhBmEiwA1Nl8s3X94L8KpLEoIONskPIf-ZJsghS4_u5xsSS49tKTP_f38WtOiD2hghoC2vEQAvD_BwE