Let's define a "target" as any unknown piece of information in a given sentence in a foreign language. It can be either a word or a grammar structure. We can divide all sentences we encounter while immersing in our target language into three groups:
0T, zero-target. Sentences that don't contain anything you don't already know.
1T, one-target. Sentences that contain one unknown piece of information.
MT, multi-target. Sentences that contain multiple unknown pieces of information.
If a sentence is 1T, you should be able to understand the meaning of the whole sentence perfectly after looking up the definition of the unknown word or reading the explanation of the unknown grammar structure. If you still don't understand it after a lookup then it's not a 1T sentence.
When making TSCs, I recommend that you only take 1T sentences and avoid MT sentences. In other words, stick to the minimum information principle. If for some reason you choose to add a MT sentence to Anki, only test yourself on the target word which you have highlighted.
A word can be highlighted in Anki by selecting it and pressing
Ctrl+bto make it bold or by setting up Yomichan to do it for you.
Having to recall several unknown words at once is very difficult and lowers your retention. If you have several words you want to learn, create different targeted sentence cards for each of them instead of putting all the words on one card. Don't fail a card because you couldn't recall a word that is not the target word of the card in question.
Needless to say, there's no point in adding a 0T sentence to Anki. You won't gain anything by making it into a card.
Learning through targeted sentence cards proves to be fast and efficient. Ajatters often refer to it as "picking low-hanging fruit". As you progress in the foreign language, 1T sentences become 0T, and sentences that were MT turn into 1T and become ready for learning.
Finding 1T sentences can be challenging in the beginning. This is partly the reason why we recommend learning basic vocabulary from a premade deck to "unlock" as many 1T sentences as possible. Keeping a large bank of sentences is another good approach. The best sentence banks are made by converting anime and dramas to Anki decks with subs2srs. You can also download a collection of premade sentences from here.
Note: Often people use terms "1T" and "i+1" interchangeably, though they mean slightly different things. The term "i+1" was coined by Stephen Krashen as a part of his Input hypothesis. It refers to a level of input that is slightly above the learner's current level.
Krashen called this level of input "i+1", where "i" is the learner's interlanguage and "+1" is the next stage of language acquisition.
"i+1" input contains unknown pieces of information whose meanings can be inferred entirely through context, while "1T" implies that there's a concrete sentence that can't be understood until one particular piece of information is looked up in a dictionary.