Know how you're getting to and from your destination before you start drinking. Whoever you're planning to drive you should not be doing any drinking at all, not even "one or two drinks," since that mindset quickly deteriorates and leads to a dangerous situation.
Eat before and while you're drinking so you don't end up getting more drunk than you can handle.
Determine your limits and stick to them. Make a pace for yourself, such as drinking no more than one or two drinks in an hour, so that you stay in control of yourself and your drinking at all times. You'll also find that pacing yourself makes the drinking more enjoyable.
Keep track of the number of drinks you've had so you know when it's time to quit. If you decide that it's time to stop, actually do stop and don't simply accept drinks because someone offers them to you.
Know what you're drinking and if you're unsure don't drink it. Also, stick to one kind of alcohol since mixing different kinds of liquor is unsafe and can lead to alcohol poisoning.
Continue to be responsible the day after you drank by making sure that you don't operate heavy machinery or aren't in a position where you're responsible for critical decisions since alcohol impairs judgment even during the hangover period.