KCDW
I use rudder trim quite extensively, especially on nav flights. I've found that it saves a lot of wear and tear on my legs and does'nt fatigue me as much as sitting pressing on the rudder pedals constantly.
Mixture is not just a case of fuel conservation but also affects the aircraft engine. I do adjust the mixture at the top of the climb and on descent (or any other time I change power settings). You may want to read up about this a bit more in your text books.