The 738s that I fly usually need a bit of left rudder trim on takeoff and some right trim as we climb into cooler air. According to Boeing it's caused by the contraction of the control cables as the aircraft cools and should not be trimmed out. Some pilots are quite happy to sit all day with the control wheel skewed but I always trim it out. We're supposed to select HDG to assure the wings are level but I do it in LNAV provided we're not turning.