As an example, if you have been shooting 1.0u and need to fatten the dose, you would be shooting between 1.0 and 1.25u. To skinny the dose, you would be shooting between 0.75 and 1.0u. If you look above the photos of the syringes in the "New to the Group" sticky, there's a numerical interpretation of what "fat" and "skinny" mean.
You don't want to fatten or skinny the dose unless you are zeroing in on a good dose. In the beginning, it's best to stick with the protocol regarding increases or decreases.