Sentence Mining
Simply put, sentence mining is the act of learning vocabulary from the content you're using to immerse. The idea is to put sentences containing a single element you don't yet know into your flashcard deck.
We suggest you stick to a single unknown element (i+1) because it requires less cognitive load to memorize a single piece of information. It also helps prevent misunderstandings, which can turn into bad habits later on.
Practical Example
We're going to assume that English is your native language, or you're at least very proficient in it. It helps to see an example in a language you already understand.

Let's pretend you're an English learner who has just encountered this sentence. You understand every word in this sentence except for hospital. You use your resources and figure out what it means. You re-read the sentence and it makes perfect sense. This is a great candidate for your flashcard deck.
The Card
The card should be structured as follows
Front | Back |
---|---|
Sentence | Definition and/or explanation |
... | Contextual information |
You can add any information to the card that helps you A: comprehend and B: remember. Just make sure to add this contextual information to the back of the card. The front of the card should be testing your comprehension and recall.