1. Routine, you will hear this a lot here, and likely everywhere else. You cannot learn a language well taking one lesson a week with no practice in between. Stimulate those neural pathways. When you have a lesson the information goes into your short term memory, but you don’t want it there do you?
Repetition, ideally spaced repetition is what you want. There are lots of systems for this, all kinds of theories, you could easily spend more time on picking a system to following (or creating one), than actually learning the language. Personally, I have always favoured the anki program. It provides targeted spaced repetition, with the words reoccurring in your deck sporadically depending on how easily you recalled the word the last time it appeared.
2. Practice listening, There is nothing like hearing a native speaker. Intonation, accent, flow, these are things you will need to master. It’s all well and good learning how to say “I have a green bike” on duolingo, but will you understand the phrase in any kind of context? What if they rephrase it slightly? Can you adapt and comprehend quick enough?
You know that movie you’ve watched 100 times (your love for Twilight is safe here, don’t worry) and know word for word? Know watch it in your target language. First of all, you know roughly what is being said and what is happening, you will quickly pick out the words you know and gather the meaning of the surrounding words through context. Second, you wont get bored, or lost, it’s a film you love! Finally, watch out for those idioms! They are so important to learn, really.
3. Practice speaking, I think it almost goes without saying. Practice makes perfect after all, and there are lots of ways to do it! Pen pals, or the more modern form, through apps and forums where you can write to each other, maybe exchange numbers or skype call, as I have often done myself. Just, you know, be careful... The only problem with this method is unreliability, I would say 8 times out of 10 people lose interest in practicing the language after a day or two, you schedule a call with them, they don’t show up, after all, they aren’t obliged. This is why I consider this method a side hustle, your primary practice should be through regularly scheduled lessons.
4.Stop worrying about grammar rules so much, it comes with practice of the language, not memorising the rule in your native language! I can’t count how many times i have been speaking and magically added the correct preposition or suffix, or form purely by ‘feel’. Listen to enough of the language and you will develop a sixth sense for it, It just feels right.
5. Join online communities, they are a goldmine for help, resources, people to talk with, WhatsApp groups are also useful, although you are likely to see some indecent images in the chat there as well.. But maybe you like that 😉.