You can dry cut by 0.125mg by cutting your pill in quarters. It's near impossible to cut any smaller, but another option is to crush a quarter, split it in two piles, and eat one by licking it up with a finger. Weird I know, but effective.
Or you can do a very simple 'liquid titration' by mixing that quarter with a cup of milk and drinking half, saving the other half for the next day. These two methods will allow you to reduce by .0625mg, or 1/16th of a mg.
As for the rate, you can cut every week or two, or longer if needed, but usually longer isn't necessarily of much benefit.
Hope this helps!