Alcohol is a tricky one. What type of drink do you usually go for? I ask because different types of drink have different effects. For instance, cider is generally very sugary. A pint of cider would probably raise your blood sugars at first, and then the alcohol would make it drop later.
I tend to only drink dry white wine now. According to the book Carbs and Cals, a typical 125ml glass will have 1g of carbs. That way I'm not worrying about trying to cover going high with insulin and then crashing later, I just need to keep some glucose to hand if my blood sugars drop a bit.
Probably goes without saying, but the more you drink, the greater the effect will be! I would suggest having no more than two glasses of wine (not dessert wine, they tend to be sugar fests), and then test your blood sugars an hour later to see if the alcohol has affected things. Testing more regularly for 24 hours afterwards is also a good idea, as alcohol can stay in your system for longer than you expect.