I was intimidated the first time I tried spending an entire day in solitude. Putting some structure on the day helps. Here are some suggestions.

Spend a brief time getting ready the night before. Ask God to bless the day, and tell him you want to devote the day to him. This day is your gift to God, but of course even more than that, it is a gift God wants to give to you. What do you need the Lord to give you: A sense of healing and forgiveness? Conviction for an apathetic heart? Compassion? A renewed sense of mission?

Arrange the day around listening to God. Here's a format I've adapted from Glandion Carney's book The Spiritual Formation Toolkit:

8:00–9:00 a.m.
Prepare your mind and heart, take a walk or do whatever will help you set aside concerns over other tasks. Try to arrange your morning so you can be in silence from when you first wake up.

9:00–11:00 a.m.
Read and meditate on Scripture, taking time to stop and reflect when God seems to be speaking to you through the text.