Disclaimer: Before I answer this, please note that this is based on my own experience as to how I take notes. People all have different strategies as to how they take notes, and this is mine. You can choose to follow it if you want to.
Okay, now let's get on to it.
1. Only take down the important concepts. Don't try to get hold of every little thing, since those are unnecessary. Only take notes of the portions you think are necessary to study, or else you'll miss out on the next important portion, which you'll regret after.
2. Be organized. If you take down the notes needed and later come back to review them if the notes are messy and all over the place, you won't be able to read them properly. It is completely fine to messily take notes when the teacher is moving quickly, but make sure you still make them readable.
3. Be an active listener. It is told that our minds can process thoughts faster than they can be spoken. Even though you might not understand the concept at first, listening to the explanations and the examples that the teacher might give to you would immeasurably increase your understanding and remembering the content.
These are my three strategies as to how I take effective notes.
I hope this helped you!
~Jinachi~