Not a recipe for every engineer, but most commonly applied math I find
is simple algebra and a little geometry. And for me a fair amount of Laplace,
albeit that's primarily algebra. And with analog increasingly sampled data
Z transform helpful, but again that's mostly algebra in application.
School was highly theoretical. I found that my best learning, like former poster,
also visualization, add to that solving a practical problem. I also now rely heavily
on Mathcad, Spice, to do the heavy lifting. Not ideal, but fast. I have also
noticed more recent physics and EE books much better visual practical examples.
One technique I am not proficient yet is signal flow graphs. They inherently
lead to an understanding of what circuit elements have significant impact on
signal flow. Additionally the algebra is canonical in many senses, getting at
a T(s) for example very rapid, vs traditional methods of node and loop equations.
One area that comes with experience is relating math to time domain results.
In the backward direction, meaning observing time domain signals and knowing
how its related to the frequency domain. Eg, phase margin, transmission line
behavior......
Regards, Dana.