Can you suggest a way to understand and develop the right habits? Or Any good method to improve code quality at personal and team level?
Would be really useful for my case.
Anecdotally, having at least one senior developer on a team dramatically changes the long-term prospects of a project, even if they are not the ones actually leading the project. I would be curious to hear other's experiences, to see if that generalizes.
(with the caveat that not all senior devs had good habits)
From the beginning? Not. That's completely counterproductive.
The first thing you have to do is be sure that you are testing the correct thing. Only after it you write your tests down.
Specs come before tests, and on most problems you will need to write a lot of code before your get the specs down.
Now, if you are senior yourself, probably, you can see that. But when you're junior developer it's very easily to misguide yourself by looking at the senior staff without questioning anything.
So, I'd add to your advice this. Yes, learn from senior developers by observing what they do and then read more about the topic to see if they are doing right thing. Also, try to find out what are the other approaches and opinions. Even if you don't agree with them it's good to diversify your knowledge.
It's however important to understand that principles are not unbreakable laws of the universe, but rather things that should guide you but that are also subject to questioning.