To achieve that high of an ABV your yeast will need all the help you can give it. Double pitch, Nutrient, starter to increase cell count, and oxygenation of wort prior to pitching will all help. Oxygenation is most critical for these type of brews to have success. You need to use a high alcohol tolerant yeast as most regular beer yeasts will not go that high. You may need to repitch with a champagne yeast ( or other high alcohol type yeast)after a while if the fermentation stops before full attenuation. I am thinking a turbo grain alcohol yeast is about the only one that will go that high. I have trouble getting 10% from a high alcohol belgian trappist yeast, usually comes in at around 9.3% fully attenuated after a month or two. I brew all grain though, and there are other factors like mash efficiency that reduce my theoretical 10%. You should be fully experienced in brewing regular strength beers before attempting a very strong one I.M.H.O. as any brewing procedures not performed perfectly will have a larger negative impact on your high strength brew. It takes a highly skilled brewer to successfully achieve such a high alcohol content brew, I don't hear of many this high, most are around 11% tops. For me,the logical progression is after you've perfected 5-6% brews, go to 8- 10%. Work your way up in steps. If you have success try your 12-14%. I have a red shiraz wine going now that doesn't even get that high ABV.
Also you may want to do this after you have a large supply of brew built up as these big beers could tie up your fermentation equipment for a very long time.
