Know your units Most alcoholic drinks have very different amounts of units in them. For instance a large glass of wine 250ml has 3 units and a glass of vodka 50ml has 2. so to get 3 units of vodka you only need 75ml where as wine you need 250ml. so when you go out drinking you have to roughly know how many is in each so you know how much of it you should be drinking. You also need to know your guidelines. A man is allowed 3-4 units a day whereas a woman is allowed 2-3 units a day.
A few NHS posters showing Some of the effects of drinking.