How to make code more efficient, optimized, clean, etc?

I know this isn't a request site and I'm not asking for code, but I would like to know what you guys think is the best idea, or training to learn how to make code more efficient.

- How did you learn to make code efficient?

- What are some good ways to learn how to optimize and keep code efficient?

I am trying to become a developer, and I have the skill sets in FE scripting, I just don't think I have the efficient scripting skills in order to become a developer. If you could help me out, it would mean a lot, thanks.

I sometimes make loops too long, or a script has too big of an activity on the server, and I really want to know how I can fix this and how I can make my scripts run extremely efficient and not give a game a huge lag effect.

Practice. Lots and lots of practice. And articles. And just generally find knowledge scattered around and absorbing it, like an amoeba absorbs... whatever an amoeba eats.