When you start taking voice classes you should establish a practice of notation. Most singers feel stuck when they can’t remember the exercises that worked best for certain situations. The more you can access what you’ve learned the less you need to relearn!
Once you find a system of notation that works, try to stay consistent so you can easily access your notes.
Here are a couple of suggestions:
A dedicated notebook - use colored pencils, a highlighter or sticky notes to emphasize important points.
Keep a running google doc, word doc or Evernote etc. where you label the day, what you learned and your homework - you can also post useful diagrams, pictures or videos here.
Video yourself doing each exercise once and then tag each video (ex. dynamics, warmup, belting).
Video your instructor (this is particularly easy if you use something like Zoom for lessons). Upload the lesson with your favorite video editing software (DaVinci Resolve, iMovie etc.) and cut and upload the parts that you want to make sure to remember. Then put these in one place and make sure to label and tag!
Create folders where you sort your exercises, for example one bin could be gentle warmups, another could be stretches and another could be warmups for opera. I like to divide my warmups into “anatomy, breathwork, diction, soft singing (gentle singing) and complex exercises”. If it’s helpful you could use those as your general bins and subdivide from there.
Keep all of the songs you are working on in the same place. Keep all the notes on the songs you’re working on in the same place.
It may sound simple but this will end up being a huge time saver and a great way to feel in control of your knowledge! A few extra minutes a week can really be meaningful later.