Paid workshops with international tutors
I'm a relatively recent convert to paying hundreds of pounds to do workshops with visiting tutors. But I would recommend it, even if you feel you'll be a bit out of your depth.
The first factor is that it's just so brilliant to see how darn good these people are with polymer.
The second is that you'll pick up a hundred times more information, tips and tricks from them than you ever will reading a book, or watching a free youtube video.
Lastly, you may not be remotely interested in the actual technique they're teaching; what you'll do is take away all their techniques, ideas and developments, and turn them to whatever end floats your boat with a renewed sense of all the myriad possibilities.