Fonty
Yes Tama girl it's great preparation. I don't think as some do that preparing for a fast is necessary, but preparation can make the fast go more smoothly. I would reccommend preparing on a raw diet (juice fasting qualifies as a raw diet) before fasting. Even just having a fruit meal as your last meal before a fast can be helpful, but the longer you can do it the more benefit to you.
If you wanted to prepare fully for a fast it would be proper to eat raw foods until your appetite went or you entered a healing crisis naturally. The raw food diet will trigger a healing crisis in time and that is the natural time to begin a fast.
However psychological factors and motivation come into the equation too. The best time for us to fast is when we feel it would be most likely to succeed. If that is after a big day of eating all the foods you crave and a big four course dinner then that is what works best for you and do it. It is not dangerous to start a fast after eating badly, it is only dangerous to break a fast with the wrong foods.
Andrew.