Do keep in mind that I'm not one of those incredible people who speak 5 or 6 languages fluently - but I have managed to get enough skills in the appropriate areas to handle my needs. These are, mostly, reading archaeological papers about textiles - which can be done with just basic understanding of the language, passive skills only, the necessary special vocabulary and the enthusiastic use of (online) dictionaries. Reading about other topics, especially scholarly material that is not as down-to-earth as archaeology reports usually are, will require a higher language skill.
So, here you go - my insights about language learning:
- Find out what you want, and aim for that. If you only need to read-understand things, it makes limited sense to get a conversation course. For reading understanding, I have had good results with getting a basic overview about the language through the first chapters of a beginner course book, then switching over to actual reading. I learned how to read Middle High German and Swedish by getting a book in the original language, plus the German translation, and reading those in parallel with, again, enthusiastic use of a dictionary to support word identification. (The books were the Nibelungenlied, by the way, and Ronja Rövardotter.) I'd consider a book optimal for this approach if the original was written in your language of choice, and you already know the translation of the book, and you love it.
With this approach, you can end up with fairly good reading skills. You will probably be quite helpless when trying to understand spoken language, though, and your active skills will be somewhere around zero, not just because of lack of practice in actively using vocabulary and grammar forming sentences, but also because pronounciation is actually a thing in most languages. - If you are going for active skills, get started on them at once. This means actual conversation with actual people, at least in written form, better in spoken and written form. Whether you practise with a study buddy or with a teacher, or talk to your cat, or to your chair - as long as you form sentences and talk about things, it's good. Best is, of course, a native speaker teacher who is willing and able to correct you, but anything is better than nothing. There's platforms online where you can look for a conversation partner or study buddy, if you don't happen to have a native speaker among your friends who's willing to have their mother tongue smattered.
- This also means that a book course by itself, or a computer course with no additional real-life real-time interaction will probably not be the best choice for learning a language for active use. Though these can be very good tools to learn grammar, vocabulary, and phrases, my impression is that these courses then tend to build up a repertoire of fixed phrases that you will be able to understand and use - but no real language use practice.
- Speaking of practice: I find it easiest to learn a language when there's a use-case for it, and when the topics interest me. I do not need to learn how to order cask-drawn beer as opposed to bottled beer. I am vastly interested, though, in learning about different kinds of chocolate, climbing gyms, bicycles, and tablet weaving. So ideally, your conversational partners have similar interests, and you can stumble your way into the new language through topics that have relevance and value for you.
- Try to do something every day. Instagram, as I've recently discovered, holds a wealth of hashtags for language learners - giving you lots of small posts with images accompanying snippets of language info. Which is just brilliant for learning a little bit every day. Films and Youtube videos are also a nice way to learn, with the added bonus of hearing actual normal people speak the actual spoken version of the language at more or less normal speed!