1. Rudder Trim. Your feet are less sensitive than your arms, so carrying an out of trim rudder force is less noticeable - unless you're talking about an aeroplane on asymmetric power. However, use it to keep the ball centred with no residual foot loads and your flying will be more comfortable. Plus your heading will be less likely to wander on a navigation exercise.
2. Mixture. In the UK, there is normally no need to adjust the mixture below 3000 ft UNLESS you have an operating CHT gauge. Most Warriors don't have one, those that do (or have EGT gauges) often have U/S installations. The old trick of pulling back the mixture until the onset of rough-running, then pushing it forward a bit can do a lot of harm to an engine at high power settings UNLESS THE CHT CAN BE MONITORED!! I've had to replace a 'cooked' cylinder pot on an otherwise sound engine which had only done 600 hours because some idiot leaned the mixture excessively. Fuel is cheaper than engines - leave it at fully rich below 3000 ft unless you can monitor the CHT!