>>12505803This, especially with definitions and main theorems. In particular, I like to rephrase certain definitions and results in my own words, so as to make them more intuitive in my head.
*Always* do a reasonably dense subset of the exercises, and I do mean *always*. Neglecting them is perhaps the rookie mistake with the worst consequences of all.
Finally, don't just stick to one book when several exist - maybe books A, B, and C work well as complements of each other. Try to find the right combination by means of experimentation.
Hope this helps. Merry Christmas, anon.