Manufacturer suggestions (paraphrased): Check your Tesa micrometer periodically to see that the zero lines up. Use a gage block to verify readings.
After heavy or prolonged use, it is recommended that the micrometer be cleaned as follows: unscrew the quick-drive end cap, as well as the thimble. Clean each part with an appropriate liquid (alcohol, naphtha) and reassemble. Lightly lubricate the spindle with a high quality oil. Eliminate any play in the thread by using the supplied setting key.
A more detailed maintenance brochure comes with the micrometers.