The single biggest thing you can do is to cut out alcohol, full stop.
You do not say the severity of your liver complaint and the extent of the damage.
Milk Thistle has its adherents, but scant evidence to support its value. The same thing applies when people speak of antioxidant foods and all that - plenty of proponents, but little actual evidence.
I am surprised your GP has not given you any dietary advice, but generally following standard healthy diet guidelines could not hurt.Keep fat to a minimum, keep salt to a minimum.
Unless you are drinking lots and lots of cups/mugs of a beverage a day, I doubt that drinking either coffee or tea will make that big an impact on the health of your liver.Drink whichever you prefer.
This page from NHS choices makes some general points about diet in cases of liver damage.
http://www.nhs.uk/Conditions/Liver_disease_(alcoholic)/Pages/Treatmentpg.aspx