Mathematics is English.
OK, not English specifically - what I mean is that mathematics is not a bunch of abstract squiggle notation on paper, it’s a series of sentences written in a natural language. The abstract squiggles are shorthand for those sentences.
Some might say the squiggles are more precise than the natural language words. Not true. The notation really is just a shorthand for the words, and mathematics is the study of words that have precise meanings.
Now, don’t get me wrong, notation is great and can help make connections that would otherwise be obscured by wordy prose - but it is not primal.
So, to become better at expressing mathematics, you need to rediscover the connection between the notation and the underlying sentences that they represent.
Take the following “statement”:
a = b & b = c => a = c
Translate it into:
“If a number a is equal to another number b, and b is equal to another number c, then a is equal to c”
Note that this wasn’t even a rote translation - I added in the premise that the variables are numbers. This is the kind of information which can get forgotten or assumed in notation, which could make it harder for an uninitiated reader to follow. Of course, you may also need to remind the reader what a number is and what the “equals” relation means... knowing what to assume about your audience’s level of knowledge is part of the art.
The “connective tissue” between the symbols is the language of logic. Words like “if”, “then”, “and”, “or”, “not”, and “implies”. These are the words that allow you to form statements with precise meaning, and you can improve your use of them by improving your language skills, not just your mathematical skills.
Now, I’m not advocating for writing everything out in long form, because some notation is just too good and too expressive to pass up. The point is to remember that mathematics is a form of writing, intended to be read by other humans, that they will be reading it through the lens of natural language, and that all the rules of good writing still apply to mathematics exposition.
Introduce your topic. Motivate your definitions. Clearly and precisely lay out your reasoning. State your assumptions. Emphasise important points. Give illuminating examples. Explain your thinking. Avoid trying to demonstrate your own cleverness. Summarize your conclusions.
And all of this applies doubly for oral presentation instead of written.