You need big, solid cubes. Not the tiny fragmented ice from your freezer that looks like broken teeth. Big ice melts slower, which means your drink doesn’t get diluted into a sad puddle.
Fill a mixing glass (or a sturdy pint glass if you’re a rebel) with ice. Pour in your vodka and vermouth. Stir it with a long spoon for about 30 seconds—stir, not shake. Shaking makes it cloudy and briny. Stirring makes it clear and crisp, like a winter morning.