[SleepyMyroslav]

If you need to organize your thoughts on what measurements are and how at least some profiling tools work you can pick up a book or two. I would recommend for example [1]. It is a bit heavy on C++ side but you can complement it with something relevant to your job's language.

If you want one bit of advice on optimization, I can try one: follow your app architecture closely. This is where data structures that hold all of the important data live and this is what limits what is possible to achieve on performance. A lot of learning is narrowly focused to specific micro optimization techniques leaving big picture as an exercise.

1 Fedor Pikus, The Art of Writing Efficient Programs