I am new to making sushi and have gotten the hang of rolling it with the nori on the outside.  The problem is when I am trying to cut it into individual pieces, I often end up mangling it to the point where it looks like it would be unpleasant to eat it.  Is there a trick to getting a nice smooth cut through the roll?  The first one of the day seems to always be the worst. 
ok get a very sharp knife (straight blade)   put the blade under water tap the blade on the counter to rid of excess water cut roll in half repeat the process on the two portions   make sure that you're using a long knife, and when you're cutting, don't seesaw, rather it should be one fluid motion  EDIT  or do it as the comment below says :P 