Learn ten times faster

So, how to apply this to languages?

1. make the milestones smaller

The final goal is to learn a language. Now, from not knowing a word to knowing some 10.000 words and sentences is a journey of 10.000 steps :-D
Make a list of those steps and take one step at a time.

For example.
1) learn to say the alphabet
2) learn to count
3) learn the common greetings and wishes
4) learn the 10 most common words of the language
5) learn a couple of sentences where these words are being used
6) learn how to tell the time
7) learn how to talk about the weather
8) learn to tell 10 things about yourself
9) learn to shop
10) learn the restaurant/café speech
etc.

2. Do one thing at a time

When you study a language, study A language.
Of course, as he says on the video, learning and producing are two different things, so using a language is not going to take time from learning another language, so you can upkeep your other languages by using the language; reading, speaking, writing, watching television and movies, listening to songs and radio.
Also, commit to your steps 100%. When you are studying the numbers, you study numbers and nothing else. Learn to count from 1 to 100, learn it backward, learn to count to hundred in fives and tens and from hundred to 1 in fives and tens... Move on only when you are totally confident with numbers.

3. Be constant.

it's better to use 5 minutes to study every day in a week than one hour once a week.

Richard Burton (and Paul Pimsleur) said that 15 minutes in a pass is the absolute maximum, the brain gets tired, bored and quits if you study longer times. You notice this in that when you are studying for hours at a time, you will spend a lot of time doing other things like thinking about something else when you are supposed to listen or read, or doodle something while you watch a movie etc. Your attention is not 100% for more than a couple of minutes.

4. Don't put all the eggs in the same basket

You don't know which "vehicle" will get you there. Try all the methods. Stop doing what doesn't work, do more of what works.

5. Debrief

When you make a mistake, ask what you did, and find out why you did it.
Ask opinions, ask people to critique you, ask people to suggest improvements, listen to people's explanations and practice the correct way of doing things.

CORRECT THE FAULT AS SOON AS POSSIBLE AND WORK IN THE CORRECTION UNTIL YOU KNOW IT.

It took me a lot of time to separate nous and vous. Because of "we", I thought of "vous" as we. I had to intentionally remind me of "notre dame", "our lady", "nous is we, we, nous, we, nous, we, nous..." to get my brain to change it.

Other things to mention here.

- practice all four parts of a language every day in all available ways. Make sure that every day you listen to the language, you write in the language, you read the language and you speak the language. Even if there is no-one to listen, speak it. Not just in your mind, not just whispering.
In the beginning, you can hide in a closet and repeat after some video online, but it would be better if you found a sparring partner from the first day and practiced.
If nothing else, you can film yourself with the computer camera and upload the video to YouTube. I bet there's plenty of people ready to correct your pronunciation, especially if you title your video challenging... like "a polyglot counts to 100 in ---sh" or "I bet you can't catch my error". :-D
A bit kinder way is to find a sentence or poem or so, written down and read out loud, and record yourself reading it and then compare your recording to the proper way of reading it. You could also do it with songs, but a couple of sentences from a book would be better. It's not possible with all the languages, but try to find something. If nothing else, maybe you can find a recording from the Bible. Or on Omniglot there might be a sample sentence.