I would cut out any dead branches and any rubbing branches, make your cuts with a sharp tool outside the branch collar, at a lateral branch, or at a bud. There are lots of websites on proper ways to make cuts.
Do the work now. Dormant pruning is best in your area. There is a canker(fugal) disease that like Magnolias and dormant trimming will be safer. They say to trim flowering shrubs right after they flower, to avoid cutting a bunch of the flowers off, which form in the fall on Magnolias. With the small number of branches you will be removing it wont matter. Be careful not to bump the delicate flower buds that are on the shrub now though. They are big old bud looking things.
Rubbing branches can form open wounds, this is an entry point for fungi.
Use a dish of rubbing alcohol and a paint brush to clean your pruning tools befroe trimming.