Milk is a good source of calcium and Vit D, I prefer semi-slimmed over skimmed and full fat, it contains 5g of carbs per 100ml, if you were to drink a glass of milk then you would need to test your postprandial bg levels to see what effect it has.
I just use milk in my morning porridge and for tea and coffee and very rarely now drink it on its own, if your concerned about the carb content then look for Lactofree milk as it contains around half the carbs as standard milk.