This book has some excellent thoughts on practice preparation and stretching.
https://www.amazon.com/Art-Practicing-Guide-Making-Music/dp/0609801775
much recommended.
Check out The Art of Practice by Madeleine Bruser https://www.amazon.com/Art-Practicing-Guide-Making-Music/dp/0609801775/ref=sr_1_1?keywords=the+art+of+practicing&qid=1570647913&sr=8-1 But yeah take care of yourself and just take it slow.
Or the art of practicing if you want the music version.