If something needs a sharp turn or curve then you need a smaller brush.
If it has a wider curve then you need a wide brush to cover that shading span. You might need to select the area because the brush has the gradual blend all around it, and you don't want to use more than half. So everything left over is what people named the same effect with cans of spray paint or an air brush. It is called over spray.
If you control were the paint is applied you can create great artwork.
The bigger brush you use the more of an area it will cover and add the gradual effect of blending in shadows, or shading, and it can gracefully add blush or color tints for some areas that are a shade different color.
If you try this with a hard edge brush, you are imitating a program that don't have the soft edge brush and they learned to do their best with out it. You can do that, but as long as you have the tool is is a shame not to use it.
Honestly, I don't know I just kinda plug it in and draw!
However, it's a hard, round brush 100% hardness 48 px diameter. My tablet is...set for left handed-ness? But thats the only thing I have changed, so Default Tablet settings. (I understand this is very limiting information, but I guess I don't know how to set my brush/tablet)
Find your tablet settings (should be under your control panel) and adjust the settings until it feels comfortable to use. You should be able to do this while your art program is open so you can test.
Next, get away from the hard round brush. I like the airbrush tool, but you'll have to find what you like. If you're just using the default settings, you'll need to go load the rest of your brushes. You can do this by selecting the load>brush preset from your brushes options. Load all of the brushes that come with the program. You can then delete the ones you don't use and save that as a brush pack.
Set your opacity low. Set your brush to fade with pressure. This will make it darker where you push harder and lighter where you don't push as hard (the airbrush is opposite this).
Make sure photoshop is set to apply sensitivity to your brushes.
When shading, start the stroke at the darkest point and move up to the lightest point. Make sure your strokes are shaped to mimic what is underneath them- a curved object is shaded with curved lines. Even though the lines themselves may disappear the effect remains.