Everything from phones to satellites runs on these principles. Electronics engineering books and ECE books cover circuits, signals and communication systems. Look under engineering books and GATE books.
ECE students should master circuits and signals early, because nearly every later subject and many placement and GATE questions depend on them.
Engineering and applied science reward hands on learning. Combine textbook study with labs, workshops and site visits wherever you can, and solve numerical problems regularly, as they appear in college exams, GATE and job interviews alike.
Technology and farming are both changing fast in India, so choose the latest editions for standards and practices. Pair theory with real examples from your own region, and keep learning even after your course is over.