For diet there is always the old standby of 80% fresh organic vegetables and fruits, 20% other food, little or no white stuff (like White Sugar , white flour, white bread, dairy, etc.) lower fat (try for the healthier ones like olive, coconut, and flax oil) and low/no chemicals. With tweaking for individual needs, pretty much a decent everyday diet.
Maybe add some fresh organic apples and apple juice every day before the flush, the malic acid helps soften the stones.
As far as herbs, there are a lot that are helpful. I rather like drinking a cup of a good detox or liver formula tea every night the week before a flush. Dandelion, licorice, and burdock are particularly good for the liver, but go lightly as they can be over taxing if overdone. A cup or 2 a day for a week or two should be fine. 5+ cups a day, month after month is probably not fine.
I'm sure some other folks have they're own suggestions, but these seem to work well for me.