Replacing the steppers with 0.9° versions would double up the resolution.
Using smaller GT2-pulleys where possible would help, too ( 16 tooth vs 20 tooth )
Or leadscrews with finer pitch.
Then there are stepper drivers with upto 128 microstepping vs 16 microsteps, but that's no reliable improvement.
You have to make sure, your mechanics run without play, backlash or binding to help steppers to really reach ( and hold ) these fine microsteps.
Using smaller GT2-pulleys where possible would help, too ( 16 tooth vs 20 tooth )
Or leadscrews with finer pitch.
Then there are stepper drivers with upto 128 microstepping vs 16 microsteps, but that's no reliable improvement.
You have to make sure, your mechanics run without play, backlash or binding to help steppers to really reach ( and hold ) these fine microsteps.