Some links to some advanced brief forms and phrases for the advanced shorthand student.
As you know, you need to be careful in which ones you choose to ADD to your list of those you know.
The one main suggestion I would have, is use those that you will write in the majority of your writing. If you find that you only take down sermons once in a while and not every week, using religious phrases might not be beneficial to you. However, if you listen or watch sermons everyday or even every week a few main phrases would be helpful for you to memorize.
You could learn a few new ones for special occasions. Have a "key" for these. After that occasion is over, you might forget what they were. I use to add to mine by writing them on the back of the steno book. Easy to find and easy to add to. Plus it stayed with the steno book and I wouldn't lose the "key".
If you forget the first ones you've learned, it's most likely because you don't need them. With anniversary, you will find phrases used in the 1920s (the years they were developing the system) and find that you don't need them. To keep up with at least knowing them, a quick review the manuals and books with your system is a good idea. This also helps you see how abbreviations are formed and can give you an idea if you choose to do a new abbreviation on a word you use constantly.
I would suggest practicing the basic phrases as well. I just wrote a sentence and did not use all the phrases I could have. It was "I'll teach you to make it, but I won't make it for you." I only phrased the "I'll", which is more of a contraction but also a phrase. Yes I did use the apostrophe, because I knew to do that.
"Gregg Shorthand had achieved the most extraordinary success ever attained by any system in the history of shorthand." John Robert Gregg, 1922