Your challenge is partly in the difficult task of memorizing many types of information that contain no “natural” end.
A book, for instance, has a natural end (the last page).
A subject (like Chemistry, or Math, or Astronomy) has no natural end. The knowledge is endless.
This means you’ll regularly be bumping your head against new concepts and new relationships between concepts, and it also means you have to regularly find memorable ways of organizing those concepts and relationships.
I memorize mainly technical information (stuff found in textbooks).
For using mnemonics with Chemistry and other technical subjects, using only one or two mnemonic techniques is going to limit your ability to creatively organize the endless waterfall of information coming at you.
You’ll have the best results with a sturdy toolkit full of mnemonic techniques to aid you in both recall and deeper understanding of the subject matter.
Personally, my strongest recommendation for a resource is Mark Channon’s book Improve Your Memory.
He covers pretty much all the primary techniques modern mnemonists use, and I’m pretty sure there are literally more “exercises” in the book than there are pages.
Work through it earnestly, and you’ll hone a myriad of mnemonic skills and techniques rather quickly (albeit effortfully).
That said, if I were in your shoes, I’d get a couple number systems down, and dive deep on the “method of loci”/memory palace/memory journey techniques.
And I’d pair that strongly with the chain method (aka the link method).
Since technical information from textbooks and reference resources are my primary use for mnemonics, I’ll also share my response to “If you were starting all over from scratch, how would you do it?”
For your specific purposes I think it will be helpful, but if not hopefully it at least provides you something to say “No way, Jose, am I doing that!” to.