I've been reading the book "Fundamentals of Piano Practice". (And people think I'm long-winded!!!)
A lot of the advice carries over to shorthand. You are teaching your brain and muscles how to work together, quickly, for almost-repetitive moves. Here's my interpretation. It's not quite in the order in the book.:
1. Start by listening to it done right. In shorthand, that means reading a well-written passage.
2. Before practising, analyze the structure to find the tough parts and the repetitive parts. In graded texts, that means the new words and phrases, and even new groups of outlines.
3. Start by practising the parts you find hardest. They will need more time.
4. Practise the hardest parts first. Lots of repetition of those, rather than write the entire thing out. Don't bother playing all the easy parts before them every time.
5. Start with tiny segments (two keys!) of the hardest parts, then the next tiny bit, then add them together. Each segments should include a note or two of the next bit, so there's overlap and you don't finish one segments and not know what to do next. (I can see the overlap being a bad idea in shorthand, except for phrases.) This way you can practise the hard parts dozens of times quickly.
6. The smaller the segment, the faster you can go without making mistakes.
7. Do not practise at a speed where you make mistakes. It engrains the mistakes. That's not to say never go too fast, just don't do it often.
8. Keep going through mistakes. The audience probably didn't hear it, and will hear the repeat / stutter. If you alway stop and repeat it, that's how you'll learn the piece.
9. Memorize as you learn. If you do it in two steps, you'll need two full passes. In shorthand, that means memorizing the outline, not just how to put in the sounds.
10. Learn parts hands separate. Not applicable to shorthand. Or maybe it is -- break things down as simple as possible, learn individually, then add them together in stages.
11. Proper hand position, movement, and weight. Proper posture. The proper is easier and more relaxing.
13. Get up to speed as quickly as possible. Look for things you have to change. Don't worry at this point about accuracy, since you won't repeat it often.
If you start slow and build up gradually, you will start with technique suitable for slow speed, then have to change your technique at each step. Some technique that is needed for fast won't work at all at slow speed.
Chord attack: Do a bit at infinite speed (all keys at once), then slow it down. This gets past the "speed wall". In shorthand, write the small segment out super fast.
14. Once you know what technique is needed, practise at your maximum accurate speed.
15. Stop practising when you stop improving or get tired. At this point, you're tired and using poor technique, and you don't want to reinforce it. Work on something with your other hand. In shorthand, do reading practise for a bit or theory notes or brief forms.
15. The last thing you do before quitting should be the most correct and best example of what you want to achieve, which is usually a moderate to slow speed. You will grow new muscle and nerve cells over the next few days, and this is the pattern you want to reinforce.
16. Think ahead in the piece.
17. Trust the indicated fingering.
18. Endurance requires control, which is brain power, not muscle power. Mindless repetitive practise is bad.
19. Breath well. Proper posture and diaphragm and rib cage action.
20. Learn to recognize and expect your second wind.
21. Mental play. Imagine yourself doing it even when not writing. Your brain needs to learn it, and this way you can practise on the bus. This includes visualizing the outline and the sentence, as well as how they're made. Break it down.
22. Rhythm is important. 90% of problems thought to be fingering are actually rhythm. In Gregg shorthand, that means doing it "right".
23. Do not practise when you aren't feeling well. You will engrain bad habits.