For example, if your recipe calls for an ounce of Saaz as a flavor addition and another ounce for the aroma addition, you would add three ounces of Saaz to the mash. Hops are added directly to the mash at dough-in. I have mash hopped with leaf and with pellets and the pellets give much better results. This could be because the hop oils are more exposed in the pellets through processing. Add slightly more bittering hops.
Current observations indicate that mash hopping provides almost no bitterness to the finished beer.
Thus when you move hops from the boil to the mash, you must compensate for the bitterness that is lost. I do this by calculating the IBUs that would have been contributed to the original recipe by the flavor and aroma hops and then increasing the bittering hop addition accordingly. After adding hops to the mash, the rest of the brewing cycle proceeds as normal. Surprisingly, the hops do not get in the way of lautering. I always start the lauter slowly, but have never had a stuck mash since starting mash hopping.