Basically your diet should be as good as possible beforehand, and your body removed of as many toxins as possible with waterfasting maybe, so you don't overload your kidneys with toxins.
When fasting personally I rest as much as possible and just do 5-10 mins rebounding a day.
After the fast, usual careful refeeding and probably try to build up your exercise again to get fit again, stay away from alcohol for at least a few months.
If you really want to know a lot then I suggest reading every thread in this forum from the bottom up.