Rewriting notes that were already fine
I used to rewrite my notes into a "neater" version every few weeks, and it felt productive because my hand was moving and pages were filling up. It wasn't. The information wasn't changing, only the handwriting was.
Watching topic videos I didn't need
A lot of GATE prep content online is genuinely well made, and I still watched way more of it than I needed for topics I already understood, mostly because watching is passive and studying isn't.
Untimed mock tests taken "for practice"
An untimed mock test measures something closer to patience than exam readiness. I took several of these early on and felt good about the scores, right up until a timed one told me the truth.
What replaced all three
More PYQs, fewer videos, and a rule that every mock test from here on happens with a real timer running, no exceptions.