First the basics: Fill the shot glass with crushed ice, then add the vodka. Wait for the vodka to get cold (a minute or two, feel the breeze off the shot).
To add some variation to this shot, you can decide a common taste for the vodka and use concentrated juice or syrup instead of plain ice. Freeze the juice/syrup the same way you would regular ice, then follow the recipe above.
* Vodka Lime and Sour mix frozen
* Vodka Orange and concentrated orange juice
and so on...
Good luck, enjoy this roar of cold in the heat.