I have found Wanikani great for teaching me vocabulary at a super fast rate (way faster than I've been able to do myself with textbooks and flashcards), but it is primarily a kanji teaching app, so the order the vocabulary is presented is according to the simplicity of the kanji rather than the frequency of the words.
Tofugu describes the teaching strategy here, which gives their suggested order of learning things.
Keep in mind, most textbooks and courses (especially the "learn a language in 3 seconds kind") take the opposite approach where you slowly learn small handfuls of vocab with the grammar lessons.
Building Vocabulary Fast:
Get yourself a frequency dictionary. (https://www.amazon.com/Frequency-Dictionary-Japanese-Routledge-Dictionaries/dp/0415610125/ref=sr_1_1?keywords=a+frequency+dictionary+of+japanese&qid=1555831713&s=gateway&sr=8-1) <---this is the one I use, get the cheapest edition possible. I love this one because it uses each word in an example sentence. Knowing just the first 1,000 words is enough to get me through weekly conversations with the Japanese exchange students my school in a wide variety of topics. The 5,000 words cover like 90-something% of daily speech.
Here's a free one, but it only surveys online content, and not spoken Japanese: http://www.manythings.org/japanese/words/leeds/
Input these words into Anki with pictures and sound (from forvo.com) and you should be able to learn them very quickly.
Building Vocabulary Effectively:
There are essential vocabulary lists out there (I use this one, but cut the ones I don't care for at first https://blog.fluent-forever.com/base-vocabulary-list/), so learn those first, then after that, pick subjects that you like to talk about, and learn all of the words that come up the most in that subject. For example, I know a lot of adjectives for food/cooking, and a lot about music/math, but I can't say much about politics, for instance.
Message me if you want to talk more about this, I'm always game!
Also, use iTalky to write simple sentences and get them corrected by natives who will tell you the right way to express yourself, not the academic and unnatural way. Hope that'll help you mate. Good luck!