If you're using guide numbers to calculate, then bouncing is going to increase the distance by 50-100%, and less of the light is going to reach your subject as it's scattered by the ceiling. So if the guide number is 80, I'd start by cutting it in half to 40. So at 10 feet that's f/4 (40 divided by 10 at base ISO).
But as you're likely using it as fill, it's going to be trial and error to just add in a pop of flash. Say the camera meter tells you 1/30th at f/4, you might try 1/125th at f/4 assuming the flash can add a few stops worth of light.
From there, if the flash is too bright you would have to adjust the aperture to f/5.6 or f/8 (because shutter speed won't affect the flash exposure).
If the flash exposure looks ok, but the subject's shadows, or background, or anything not illuminated by the flash looks too dark, then you'll want to lower the shutter speed. This will let in more ambient light,making the image brighter overall, but it won't affect the flash exposure (the flash is so quick, all the light will reach the sensor no matter what the shutter speed - up to the synch speed at least)