Here’s a rough sketch of my approach to language learning:

• learn the phonology
• learn the grammar
  • read a grammar book like a novel, quickly through
  • read the grammar taking notes, ignoring overly complicated matters. Your notes will be but a few pages long!
• go through a textbook to internalize the grammar, build a core vocabulary and Sprachgefühl
  • read a good textbook (Assimil, good old Colloquial or Teach Yourself) rereading the dialogues and until you remember their vocabularies
  • memorize choice dialogues, songs and poems. Some techniques:
    • just just say just say the just say the whole just say the whole sentence just say the whole sentence like just say the whole sentence like this, to memorize a whole page of text in
    • write the first letter of each word: “w t f l o e w” to use as a crutch when reciting an entire page you learned a few days ago, but remember it’s not important to remember it after, just memorizing for a single recital already etches the words and grammar in your mind forever
    • simply repeat a new word (or better yet, it’s whole context/clause) 30+ times quickly to chisel it into you brain. At 30 seconds a word, you can learn over 100 words per hour, keeping most with you afterwards!
• read
  • we can read significantly faster than people can speak, so reading gives us far higher input for our time
  • read widely, forums, novels, friends’ chat logs, subtitles etc. only looking up words you encounter often or which stick with you, your Sprachgefühl should often give you an inkling
  • Listening-Reading method - the overall fastest way to language mastery at this point, just listen to an audiobook in your target language while reading along to the same book in a language you understand (Dostoevsky, Dumas, Verne and Rowling are easy to find) The longer you can do a sitting, the better. A single 12 hour session will turn your brain to mush, but gift you a huge leap in fluency! The full system

Overall, you want to stay just out of your comfort zone on comprehensible input. Good textbooks are the best way to do this, then reading’s the fastest way to continue progressing. You can start with a textbook before reading a dedicated grammar but I like groking the system early. Phonology is important early on, to develop an inner voice and Sprachgefühl.

Most importantly, an educated native knows tens of thousands of words, idioms etc. Compared to that, learning some conjugations or declensions, some 30 letters of a new alphabet etc. are nothing, a day’s work really. I optimize for the slog of vocabulary acquisition.

Other

• traslate text, then translate it back and compare

proper time for him to read some short and easy chapter in this work, and to translate it into his native language with the utmost exactness; let him then lay aside the original, and after a proper interval let him turn the same chapter back into Persian by the assistance of the grammar and dictionary: let him afterwards compare his second translation witht he original, and correct its faults according to that model. This is the exercise so often recommended by the old rhetoricians, by which a student will gradually acquire the style and manner of any author, whom e desires to imitate, and by which almost any language may be learned in six months with ease and pleasure. - Willian Jones’ Grammar of the Persian Language

Critial period is fake.

children actually take several years to function in a language, which is often much longer than an adult that knows what he’s doing. The Michel Thomas style tapes which I alluded to above are good at giving an adult a passable diving-board for a language in about 8 hours. It can be done. You can also give an adult a crash-course in phonology and articulatory phonetics that will make it easy to understand and with practice produce the sounds children take years to master.

The motivation of a child and adult are utterly different. A language-less child has lots of reasons to invest most of his mental life in attention to language. Apathetic adults don’t.

What I really get sick of is doomer adults who cope with their laziness by talking about how hard it is to learn a language as an adult. Many adults still learn languages all the time. There is some circumstantial evidence that infants cue into some acoustic cues and other things quicker than adults, but I think in most cases we’re just looking at infants semi-consciously honing in on what details they’ve acknowledged to be linguistically relevant. In reality, developed humans have huge institutional and intellectual advantages to learn.

Learn vocab after grammar structure

This is hard for people to understand because monolingual people think that languages are just different word lists that people use. As a result, 101 students will manually look up every word in the dictionary to translate. This actually increases the mental load of learning a language because people have the idea that to speak it, they have to think of something in English, then translate the sentence word by word, then say that. What a pain.

So what is a language if not words? It really is a set of constraints as to how words can go together: what order they go in when modifying each other, but also languages are morphology. Verb endings and tenses and such are literally the most important part of a sentence. If you don’t have a productive and reflexive use of verbs, you are literally just going to be reciting nouns you know like a monkey.

This is actually why I recommend people learning Romance languages or German to use Michel Thomas’s audio. Thomas doesn’t lecture at all about what he’s doing, but he focused only on using verbs and building up basic expressions from the bottom up until it’s understood reflexively by students. To actually learn any language, this is more or less what you are going to have to mentally do anyway in the process.

You can fluently speak a language knowing only about 50 words. If you understand the “grammar” of a language, you can basically get by anywhere anytime with a couple dozen words only. What words you don’t know can easily be figured out, but you can’t wing it with grammar and you can’t wing it with morphology.