Any sentence will do, but only if you throw away the bad ones.
They'll take your time and energy. They will take away your will.
If you are having too much trouble to memorize a piece of vocabular, throw it away.
If are dubious about an aspect of the sentence, throw it away.
If you think it is too long, throw it away.
If you think it is now worthful, throw it away.
Don't worry about the kanji count. Just do your best allways, that it will rise again.