Alex is a qualified Horticulturist, Arborist and a bonsai teacher having spent 2 years learning at the pre eminent bonsai nursery and the bonsai master the late Mr. Sabaru Kato.
With pines and conifers the old needles need to be cleaned out either by plucking or trimming with your scissors. Excess needles tend to interfere with the growth of new buds and makes the trees look untidy. If the tree does not have many needles to begin with you can just pluck off the downward hanging needles.
If the deciduous trees still have leaves attached, it is quite safe to cut them off to force them into dormancy. If some deciduous have long branches that makes them out of shape: cut them back to keep the tree in proportion.