There aren’t as many filters on Clip Studio Paint compared to other art programs, but there are some interesting ones you won’t find elsewhere. Normally though, I’d use the blur filters to create a shallow depth of field if needed. This makes the background or unimportant areas less distracting. You can also sharpen some areas as required.
You can apply filters on a specific part of the image by drawing a selection. There’s an interesting filter called Correct Drawing Line to adjust line width.