Here is all you will ever want to know about it...
http://reefkeeping.com/issues/2008-08/nftt/index.php
It will have instructions and charts to reference.
You can also dose vinegar instead of vodka or vinegar along with vodka. Here is the link to a chart for vinegar dosing (its dosed similar to vodka but at a 8 times the volume).
http://www.reefcentral.com/forums/showpost.php?p=19462538&postcount=150
and a thread discussing
http://www.reefcentral.com/forums/showthread.php?t=1981622
I dose both.
What it does.. In a nutshell vodka and vinegar provide a carbon source for bacteria that consume nitrates and phosphates. Dosing vodka/vinegar to feed these particular types of bacteria can be helpful if you cannot manage nitrate/phosphate levels through feeding protocol adjustments (rinsing fresh/frozen foods, reducing quantity, etc.) and traditional nutrient export mechanisms like a skimmer, macro algae and water changes.
Dosing a carbon source does require diligent testing. Too much of the carbon source can cause a bacterial bloom that will deplete the oxygen levels in your tank (which could kill tank inhabitants) if you don't have vigorous agitation of the water to aid in gas exchange.
It works very well in situations such as mine where the tank is over stocked, I like to feed a lot and the macro algae and water changes cannot keep up with the nitrate/phosphate production.