This method I am creating as I write this makes use of the immersion and active usage aspect. If you can be constantly using a language, that would be the fastest way to improve in the language. The problem is that done improperly and it will be simply to hard to keep up with. My idea is to make use of the language in your everyday tasks in a way that is efficient enough that there is no sense of work, only usage.
The method: starting with the things you write most frequently, learn the L2 words for those words and then write those words exclusively in your L2. When you do this with the most frequently used words it stays easy to do this.
Examples, or all possible things I can think of that you should incorporate:
Date and time if you write journals or have to date anything
your name which most people have to write often
common words in writing (a, the, you, me, go, ect)
common words you write
(groceries, heating bill, schedule, gym)
So it starts off with words you will need to use multiple times everyday, so lets say your a student sitting down with a laptop to take some notes on a textbook chapter. When you take the notes, there might be some keywords you know you will need to write alot, or just the a, you, me, it, thing. In either case, as you take your notes, start looking up the L2 for common words and then from then on use those instead of the L1 words. Even make a legend for yourself if you need to and look up the L2 translation in the legend of common words and then write it instead. By the time you finished an hour of notes you will have learned some words.
Create an SRS deck and the end of the day and add the words from the legend to the SRS and review them.
This only described words when you are writing by hand but you could do the same thing with computer note taking. For a language like Chinese this will be a bit more involved. You need a pinyin input application or use an online one. After that everythin is the same. Even easier because to make a legend there are programs that can analyze some of your written documents and come up with a list of your most commonly used words ordered by frequency. You can take this and create a rough legend to go by each day. This does’nt take into acount grammar as much, it is mostly to get you touching the language anyway possible. This method is often called codeswitching because you switch between languages. I don’t think this will affect your grammar in the long run as long as you learn the right grammar eventually but this is mostly for languages with an unfamiliar writing system like Chinese where you have alot of memorizing to do and not alot of fun to be had doing so.