Here is what I recommend.
1. Center your sticks.
2. Look at the FC's monitor screen and see what value your channels are at.
3. Adjust subtrim in your transmitter until all channels are centered (except throttle--duh).
4. Take off the copter and hover. Copter may want to roll or yaw or whatever. Use sticks to counter-act. Make note of which direction you have to hold the sticks. For example, if the copter is yawing to the left, you have to hold the yaw stick slightly to the right to counteract.
5. Land. Use the trim switches (note: NOT SUBTRIMS) to trim in the inputs you had to put in with the sticks. Example: if the copter was yawing to the left, put in a few clicks of right yaw trim.
6. Repeat until the copter hovers pretty well with the sticks centered.