I am not sure if you are really looking for a way to cope with varying notations, but mostly these are necessary to name all the values involved in a document. Often, different topics deal with different sizes, all of which need a unique identifier.
The best way to cope with this is to adapt to it. In my field it is common to introduce every variable explicitely before using it, so when I fully read a document, I just need to make sure to not miss these introductions.
If you have trouble remembering, it may help to write them down for each publication etc. you are considering.
I had a problem where an author used M and N the other way round than I would have. I failed to reproduce some results, only to realize I had not properly read the paper.
This was my fault though, the author is free to define his own notation as long as he tells the reader.