I'm not sure what the best dosage would be to start with. If you're currently taking another fiber suppliment then I'd try to take roughly the same amount of fiber.
If you aren't taking anything, then maybe 2 casels a couple times a day would be a good dosage. When I first started taking them I found my BMs were more solid, but also I has more of them a day and got a little bit of cramping. I haven't had that in the past little while though.