http://www.ssrcfc.ca/trimming.html

Goldsmith trimming. If you have an iphone there is an app called the "Trim App" You can have a caller tell you what to do, for example: to check right thrust angle, fly into the wind and pull to vertical upline, what does the model do? Drift to left, straight, or drift to right. Have your caller check appropriate box. At the end of the flight, you hit "make report" and it will list suggestions. Change only one thing at a time though or you will be chasing and creating new problems.

Short answer, throttle to rudder mix.