Answer: Es importante que duermas un poco antes de la excursión.
Explanation: Because the verb in this sentence must be conjugated in subjunctive mode: tú duermas.
The subjunctive mode which is a verbal mode that expresses an action, a process or a state as hypothetical, doubtful, possible or desired.
The meaning of this sentence is that it would be desirable to sleep a little before hiking.
Furthermore, the word "excursión" in Spanish is acute, because its stressed syllable is the last one, and as it ends in "n", it must have a written accent. Excursión.
[tex]\textit{\textbf{Spymore}}[/tex]