Here are a few general guidelines I would recommend:

Make sure the wings, stabilizer and fin are aligned as squarely as possible. Look for any warps or twists in the wing. These are probably most visible when viewed from the back. Straighten the wing if necessary. Wing and stabilizer incidence should be set as recommended by the manual or indicated on the plan.

Ensure that the COG is set as recommended for the first flights. This may later be adjusted to obtain better flight performance. Generally, it is set at about 28-30 percent of the wing chord starting at the leading edge. AUW of the plane should be within the recommended limits.

Make sure all the control surfaces and trim tabs are as neutral as possible before attempting any flights. One exception to this might be a couple of clicks of up elevator trim to aid the climb and improve the glide a bit.

It is probably best to pick a calm day to trim, if possible. Look for any tendencies to veer either right or left with the sticks neutral. It should not climb very steeply with moderate power, nor should it be very difficult to hold the nose up with the elevator. A few clicks of trim should be all that is necessary to correct any minor deviations. Control should be smooth, responsive and predictable. Anything worse than that probably indicates a structural or mechanical problem that needs more attention. Your goal is to achieve straight-ahead, level flight at a moderate power level with your hands off the sticks or with very little intervention.