How to learn designing electronic cicuits?
Give your engineering school a "thumbs-up" - you've realized that your electronic education is incomplete, and never-ending.
For the practical aspect, Dave's EEblog is popular (and entertaining).
Many find "The Art of Electronics" by Paul Horowitz, Winfield Hill to be helpful in circuit design. It applies all the theory you learned to practical circuits.
Get a SPICE simulator too. A free one is downloadable for PCs:(LTspice).
And get a breadboard, and some measurement tools. Be prepared to learn from your mistakes - smoke is a great learning tool. My tin hat is on - folks are passionate about which aids helped them most, because learning is often frustrating and painful.