While you're on the ground, check the rudder and nose wheel visually and get them as straight as you can. Then take the plane up and trim it for straight and level flight using the aileron and elevator trims. Then, take the plane through an easy, big loop and watch what it does. If it 'slides' to one side during the loop, then the rudder is slightly out of trim. Adjust the rudder trim and then re-trim the ailerons for level flight again.

Always adjust your rudder trim for straight flight, not for ground rolling. Or else the rudder will kick in just as you lift off for a real surprise. [8D]