Good question! I''m not an expert and struggle to remember fast when learning French but I noticed that repetition is very important when learning languages.
We tend to read or do particular exercise only once and I think this is a mistake. We need to revisit previously read texts, etc a few times to remember vocabulary well.
I also use space repetition program called Anki. It has some limitations and should in my opinion we used only as a support tool, but it brings some positive results. There is also similar program that I used when learning English. It is called Supermemo (not sure if they have Polish courses but the software is made in Poland, so I would not be surprised).