How to Improve Signal Processing Skills? I've heard that signal processing is fundamental field that can be applied to many other fields (MRI, EEG, audio, speech recognition, communication even to economics)

So, I want to contribute myself to studying this field deeply.

I already took Signals and systems and DSP, and also in this semester, I'm taking Statistical Signal Processing.

This may be stupid question
But, I cannot form any idea of how I can improve and study signal processing.
Taking a theoretical theory is not enough to get the concept.
And even if I learned some basics, I still don't know what signal processing is in general.
Constructing a filter or classifier is main goal of signal processing?

Could you share the general insight and recommend the method I can follow?
One of the best ways is to hang out on this community.
Read questions and answers.
Try to replicate results on answers.

Once you have more knowledge, try answering questions of others.
If you encounter a question on a field you don't know, find resources to read about it until you can answer the question (Assuming it is not deep and requires deep knowledge).

Other classic approaches would be books.
Yet, I recommend Hand On approach.
Namely if you read a book, choose those which has code inside them to replicate results and have better understanding of real world models.

You may even look for some courses on Coursera:


Digital Signal Processing. 
Audio Signal Processing for Music Applications.
Fundamentals of Digital Image and Video Processing.


There are few options on edX as well:


Discrete Time Signal Processing.
Signals and Systems, Part 1.
Signals and Systems, Part 2.
Discrete Time Signals and Systems, Part 1: Time Domain.
Discrete Time Signals and Systems, Part 2: Frequency Domain.


For more classic recommendation you may refer to What Resources Are Recommended for an Introduction to Signal Processing (DSP)?

Enjoy the ride!