What works for me is, after take off, trimming rudder first (on a slider/rotary) till the ball stays in the middle, then trim the elevator (on a slider/rotary). Gain some speed and navigate till you are approaching or have reached cruising speed. You set the throttle to 90% and fly level, trim rudder, trim elevator, fine trim rudder, fine trim elevator and finally add a few key-clicks for the aileron trim.
On a single engine plane, if your speed changes, you'll need to trim, again and again.