The best way to learn depends a good bit upon if you're a self-learner or not. But here are some options:
There's the
section of the forum mentioned above. You'll find loads of info there. There's even a pinned thread called How To Design Clothing that links off to lots of info.
UtherAcademy also hosts courses on clothing design. That section of the forum
is here. Most of those courses are Pay kinda things, but if you look for a thread in that section with at title that starts with
Free class there's a link to an in-world location where I've put up some videos you can watch for free at your leisure to get ya started.
Lots of designers also teach freelance, so it never hurts to ask. Especially if you know a current designer.
RaD Fashions for Men and Women
Store Location: vww://utherverse.vww/@64021/radfashions
RaD Catalog in UVCloset
Transgender Fashions from RaD Rand's Learning Zone is now open ... and Free! Location: vww://utherverse.vww/@64021/tlz