One major issue to tackle while learning a new language is the problem of forgetting what you have lave learned previously. 
The primary solution to this is to understand the fact that you learn a language and that is a process. Many of us don't learn a language just to pass an exam or even if we need to do that there is a fundamental reason behind that: studying abroad, working abroad, or immigration. 
Given that, it is not practical to just study for an exam for the sole purpose of memorizing some items, hence we need to consolidate the knowledge of another language to be able to use it in the target social ground and that is not a goal but a process in progress.
Being constantly present in the process of learning is against forgetting what you have learned since you don't memorize and thus understand and use and this becomes a habit and practicing this over time makes perfection!

Consider learning a language like a project which needs a gradual upgrade over time.
With this, you train your cognition to be habituated to this never-ending project.
Cambridge Cognition website defines Cognition as such:
The mental action or process of acquiring knowledge and understanding through thought, experience, and the senses. 

With this being said, language cannot be memorized, some elements might but not the entirety of it. Furthermore, I'll advise learners to keep making learning fun for themselves and gradually a habit, there is no one right or wrong way. You must figure it out on your own terms. anything can work and is possible as long as you are on the track. once you crack the code of what works for you you're already on it. 
This might take time or become frustrating, some guidance can facilitate it for you so don't be shy and ask teachers your friends, and peers. 

But remember, NEVER GIVE UP!






references:
https://www.cambridgecognition.com/blog/entry/what-is-cognition