Language learning is a marathon not a sprint. The majority of people give up before reaching their goals. With this in mind, you should think carefully about how you will keep your motivation up and how you will make the process fun and interesting all the way through. Don't expect it to suddenly get fun when you reach a particular level. Lots of people put up with boring study now in the hope that there'll be a magical point in the future when they are actually good enough to do the thing they really want. Just skip the boring part and start doing the thing you really want to do right from the beginning.
When choosing a teacher, think of them like a coach. They'll give you guidance, encouragement, correction and explanations, but they won't do be able to do the work of learning tons of vocabulary for you. You have to find a way to get all that stuff in your head, just like an athlete who has to find a way to wake up early and jog for miles everyday.
Start with spoken language. Spoken language is the ground truth of a language. Writing has additional layers of culture, class, snobbery and education. Speech is pure grammar flowing out of people's mouths. Try to find TV shows, podcasts, youtube channels and so on where you can listen to the language and get a good feeling for the sounds and rhythm. Try to make sure you listen to a reasonable amount of unscripted conversation. Hollywood movie scripts are too perfect. You need to get used to all the "umms" "errs", sentences that change direction half-way through and so on.
If I had to lay down a more specific plan I would say do something like this:
* Go through an audio only language course like Pimsleur.
* Start watching TV shows, movies and videos in the language. As you watch, pick out words and phrases that seem to pop up a lot. Look them up and put them in flashcards/a notebook/an app so you don't forget them. You'll notice that you pick up the meaning from context surprisingly well on occasion. (It's very easy to work out a phrase like "Run away!!" in an action movie, for example)
* As you build your vocabulary you'll start to notice chunks of language together and patterns. Study a basic grammar book to help understand how the phrases that you already know are put together.
* Keep doing this process regularly for months and years. You'll get to a point where you more or less know all the words, and you'll have learnt them in common, natural phrases and sentences.
Some pitfalls to avoid:
* Hyper-optimising the language learning process and endlessly trying new apps, software. Sure, it's fun to write a script that grabs words from X and puts them into beautiful flashcards in Y, but really you only need to learn 10 words a day steadily for a couple of years, may as well just write them by hand.
* Trying to race through lists of the 10,000 most common words. No context, no grammar. Very boring too so most people give up.
* Translating everything to your native language all the time. At the start, translation is necessary, but even simple concepts and words don't map neatly between languages. It's best to avoid your native language as much as possible.
* Focusing on the written language over the spoken language. If you goal is to read and write, no problem, but in reality spoken and written languages can be quite different.
* Asking "why" too much. Sometimes an explanation can be helpful but often the answer is "That's just how people use the language". Getting hung up on the thousands of strange rules and inconsistencies in a language isn't helpful. Just listen, copy and use!