I was taught to fly with a little bit of down trim. This gives the plane a built in tendency to avoid stalls. For the pilot, relaxing a little bit of back pressure to allow the plane to descend is a smooth way to bring a plane in. When you flip the plane for inverted flight, the down trim is also a built in reminder as to which way is up, because now the plane will be climbing.
As you gain experience and transition to 3D or pattern, you'll want to fly with nuetral trim...but bear in mind that for some types of flying down trim has certain advantages.

For planes with flat bottom or cambered airfoils, setting the wing at the proper angle will greatly reduce the need to trim and re-trim the plane for different airspeeds. I've seen ARFs that you would expect to be totally R&D'd and wrung out by the MFG that needed the wing's trailing edge raised a considerable amount.