Read, Write, Speak, Teach, and Repeat the process.
This is my simplest answer.
For long-term memory and a more lasting learning experience, I would add: find meaningful and personal connections to any or all of the areas of the language you are studying, so they are applicable to your daily life.
Hi, okay, I don't have any perspective on this question "how to learn a new language ":) I think just for talking ,for communicate with somebody who speaking foreign language, Cuz I like it, if you wanna me give you an example,it's about culture and curiosity about new things.The most direct way is use the native language talking ,reading and learning. hahaha