How to drink responsibly?

I find that when I go out I always seem to drink way too much. Its not that I am an alcoholic at all; i only drink during the weekends and do not 'crave' alcohol when I am not drinking. My problem is that when I do drink, I keep drinking more and more and this leads to a blackout (and an empty wallet) much more than I would like. What can I do to stop drinking so much each time that I do drink?