The book “Refresher Course in Gregg Shorthand, Diamond Jubilee Series” by Strony, Garvey, and Newhouse has many useful exercises for writers of Diamond Jubilee. In particular are several blocks of outlines that illustrate phrasing, joining-forms (ligatures?), brief forms, and frequently used words and phrases. There are about 1750 items in these blocks, and about 1350 unique ones; many are duplicated, some several times, in multiple contexts. I wrote them all out in longhand on seventy-five index cards. I shuffle them and do a few at random every day, usually first thing in the morning when my mind is fresh and breakfast is cooking (yes, I am a lark). “Doing” a card means that I read the longhand, write the shorthand, then check my results in the book, correcting my mistakes and usually just copying out all the outlines from the book again for extra practice. I didn’t write out the correct outlines on cards, preferring to do that repeatedly during my practice sessions.
If you’re comfortable running software from a terminal or console window, there is a very nice, free scripting language called “wolframscript” that you can get here https://www.wolfram.com/engine/. I copied my cards into a script here https://gist.github.com/rebcabin/bcd85e31c41c6ae8c921c6d5ce56e742. The instructions for using the script are at the head of the file. This is handy for popping up random cards on the terminal screen and driving your practice. I don’t, yet, have a way to display Gregg on the screen—that’s aspirational—so you will need a copy of the book if you want to follow along. It’s readily available from Amazon (e.g., here https://www.amazon.com/Refresher-Course-Shorthand-Diamond-Jubilee/dp/0070622051/) and from Ebay (e.g., here https://www.ebay.com/itm/REFRESHER-COURSE-IN-GREGG-SHORTHAND-DIAMOND-JUBILEE-SERIES-By-Madeline-S/183910712475).
At this writing, 24 Aug 2019, they are a bit pricey: $40 and $62 respectively. However, they pop up now and then at lower prices. I think I got mine for eight bucks. I do not know if the book is available online at any price. My experience is that books on Diamond Jubilee Series are only available in paper form. I prefer that, anyway.