I've never had much success learning from flash cards or other self-studying. Repetition & usage in conversation is the key. Or for instance if I read a news article where the word is used, then look it up, and see other articles within the next few days that also use the word. That's a really good way to remember.

I prefer learning new words with phrases, so I can learn a context to use the word. I try to find a book name, a movie title or a song extract where that word is used. Then, I create flashcard with these phrases. Hope it helps

I think you need to combine strategies. For instance, some words need to be learned with some mnemotechnics, because they are hard to memorize or its meaning is hard to grasp despite being common words. Spaced repetition has a base but it lacks context. So it is better to read articles from newspapers and you'll notice some words are repeated and you don't know. Those are the ones you should pick to learn.

I've heard good things about using flashcards, and that's what I plan to concentrate on next. I have tried them while learning Italian, but haven't really taken them to work with daily practice. I agree at least on the idea (that is being promoted on the site that I'm linking to below), that flashcards are better if you make them yourself, instead of taking someone else's set. https://fluent-forever.com/create-better-flashcards/ https://fluent-forever.com/the-method/vocabulary/base-vocabulary-list/

It is very hard to remember words without context. I would advice anyone who wishes to learn new words to try storytelling.