Retreats are often very intense experiences. They are immersive in nature. A retreat should offer no alternative to escape into mundane distraction and idleness.
Solo retreats can be even more intense. You don't have the support of other practitioners around you. You don't have that companionship and the ability to simply share a cup of tea. Those seeking to go on a retreat into solitude should prepare themselves.
Is your practice strong enough that you can be self-sufficient without the guidance and support of your teacher or fellow students?
Know how to work with resistance and uncertainty.
How will you work with doubt and uncertainty on your own? How will you overcome emotional uprising and commotion?
A retreat is not a time to work with illness or disease. Enter the retreat in a healthy state of body and mind.
Free yourself from mundane activities.
You are entering retreat with a strong intention. You are committed to the practice and have isolated this brief moment in time. Don't waste it checking your email, social networks, calling and texting your friends. Pay your bills before the retreat, stock up on food and necessities and identify those moments when your mind is grasping for something to entertain it.
Be decisive about the view.
Understanding the view, all practices fall into place. Doubts naturally free themselves and problems arise as opportunities to let go. Resolve all doubt and uncertainty regarding the view with your teacher, when you are confident in the view you are ready for retreat.