I’ve learnt some Spencerian from Michael Sull, but he has a book that is specifically for American Cursive:
The Art of Cursive Penmanship: A Personal Handwriting Program for Adults https://www.amazon.com/dp/1510730524/ref=cm_sw_r_cp_api_glt_fabc_WAQC5RPT21SZ521SDM50?_encoding=UTF8&psc=1 which might be a good resource.
Check out a workbook like this.
But for an easy exercise to get started, practice your loops and lines. The foundation of beautiful handwriting is consistency, and this will help standardize the width and slant of your letters.
Based on your other comments, it sounds like you might just need to get a workbook and take the time to practice a specific style. The current American handwriting is just "American Cursive" Michael Sull has a workbook on Amazon called "The Art of Cursive Penmanship" but you could also go with the Palmer Method, which would be what your grandparents or great-grandparents learned depending on your age. There's a link to Palmer in the About/Free, Useful Resources section of this sub.
Mine was abysmal and I took a little bit of time each day to work through a set of 5 Spencerian copybooks I got off of Amazon and it made a huge difference. There are a ton of free printable resources for it though.
Pick a style and spend 10-20 minutes most days practicing. It takes some time to get going, but once you start noticing improvement the payoff is big.
This is a really good book on handwriting for adults.
Here are some examples from about a century before Kipling.
- George Bickham's "Round text, a new copy book https://books.google.com/books?id=UEJfAAAAcAAJ&dq=george%20bickham&pg=PP17#v=onepage&q&f=false
- The Young clerk's instructor, also by Bickham [1788] https://books.google.com/books?id=GAVQAAAAYAAJ&dq=copy%20book&pg=PA2#v=onepage&q&f=false
If you can get a copy of it, George Bickham's "Universal Penman" is filled with precisely the stuff that Kipling was talking about, all written in the most exquisite handwriting.
Three more books that I have found useful [but contain less "copybook headings" are]
- Huntington's Art of Penmanship https://books.google.com/books?id=PwxQAAAAYAAJ&dq=penmanship&pg=PP1#v=onepage&q&f=false
- John Jenkin's art of writing https://archive.org/details/artwritingreduce00jenk/mode/2up
- Michael Sull's "The art of cursive penmanship" is also worth a look, https://www.amazon.com/Art-Cursive-Penmanship-Personal-Handwriting/dp/1510730524 as is this set of Spencerian copybooks https://www.amazon.com/Spencerian-Penmanship-Theory-Book-copybooks/dp/088062096X/ref=sr_1_1?dchild=1&keywords=Spencerian+Penmanship+%28Theory+Book+plus+five+copybooks%29&qid=1600840431&s=books&sr=1-1, (iirc Spencer's manual is also available online)
Try thisThe Art of Cursive Penmanship