For well-seasoned chicken breasts, salting the top of the skin isn't enough; you need to get some under the skin as well. Though wiggling your fingers in between the meat and the skin can get the job done, it can be a little awkward, and Cook's Illustrated has devised an easier, neater approach.
Photo by Steve Johnson.
To get your salt and seasoning as evenly distributed as possible, Cook's Illustrated recommends separating the chicken skin from the meat, then gently peeling it back, leaving it attached at the "top and bottom of breast and at [the] ribs". Sprinkle on your seasonings, fold the skin back in place and cook as usual.
The Best Way to Salt Chicken Breasts [Cook's Illustrated]