There are two ways of getting the most out of your Attribute Elixers. One is to wait until you get to a save point. Save your game, then use the elixer. If you don't get a high gain, simply reload and try again. As this can take a long time, another way is to save them until your risk is at max. Exit battle mode and use them. Since this is when the computer considers you most vulnerable, it greatly increases your chances of getting high attribute gains.