That is a very good question. I struggle myself with remembering words and phrases easily. Nothing seems to work well :/
I can recognize the words, but it is difficult to produce them in the conversation.
I think that practising the language every day is the key to remember words fast. This is how we learned our native tongues, right?
use the words in your daily life
like pawel says, practising every day or at least very regularly will help you remember.
for remembering the vocab on here i would add them to flashcards (ulangi is a good, free app you can add words you're learning to).
A great way to remember vocabulary is to use small, colourful sticky notes that we hang above our desk, bed on the fridge or in places I frequent. A good way is to stick these sticky notes with the translation of the word to a specific object, for example, I stick the sticky note with the translation "szafa", on the wardrobe door, "lustro" on the mirror.