Stainless steel braided lines, clean the caliper inside and out. Rebuild the master cylinder..New Brake pads.
My CB360 had crappy brakes, after the addition of lines, and a rebuild, new EBC pads, the brakes are pretty good for an old 1 disk system.
I believe the CB550 has the same or similar single disk. New pads, and deglaze the disk might make a significant difference.