Hand Blowers
Hand blowers are helpful. They can blow dust off lenses but are
also used to blow dust off sensors. When blowing dust off sensors I
find it wise to make sure to blow out whatever is in the blower
before blowing on the sensor lest you blow residual dust on the
sensor, which I have done. Worse are hairs that tend to be
attracted to the rubber on some blowers and can work themselves
inside the blower... ending up, you guessed it, on your sensors.
Hairs can also suddenly appear inside the camera, not on the
sensor, but wedged in a crack between the sensor and the outside.
A fine pair of tweezers (not touching the sensor) can remove them.
Step-down Rings
Step-down rings allow you to repurpose one filter or another by
stepping it down to fit a smaller lens. Otherwise you need an
expensive filter (such as a polarizer) for each size lens diameter
you might have. Typically the smart move is to buy filters in the
largest size (say 77 mm) and then use just one filter with a series of
step-down rings to fit the rest of your lenses.