Correct Translation: It's important for you to sleep before the trip.
The sentence above is incorrect because this isn't the present subjunctive form of the verb 'dormir.' Remember that some verbs are stem changing verbs and ir → ue. The correct verb form is duermas.
'dUErmas' → [verb 'dormir' - present subjunctive - 2nd person singular ('tú' = informal 'you')
