In plain words
Through sleep, and through thoughts and the rest, the mind day after day grows dull and falls into ruin. Wake it by effort. Do not let it wander off. Keep it in its own state, and keep it there more and more.
Word for word
Through sleep and through thoughts, the mind repeatedly becomes obscured and loses steadiness. Awaken it through effort, keep it from wandering in its own state, and establish it there again and again.