In the three languages I know somewhat well, it's pretty easy to split a long sentence into shorter ones, which is a a way to avoid tedious flash cards. In Japanese, however, I find that I am not yet at a level where I can intuitively tell if my splits result in what would be considered complete sentences, probably because of the tendency in Japanese to leave out the subject. Note that the shortening is to learn vocabulary rather than grammar, so if a grammar point disappears it's not a problem unless it renders the sentence faulty in some way.
Let's take one of the first sentences in Botchan as an example:
This is definitely too long to be a good flash card sentence. Could I split this into:
(or the shorter 学校の二階から飛び降りる。?)
(perhaps even 一週間ほど腰を抜かした。?)
The English translation could be split (and slightly altered) into two complete sentences:
I once jumped from the second floor of my elementary school and was laid up for a week with a dislocated hip.
I once jumped from the second floor of my elementary school.
I was laid up for a week with a dislocated hip.