Use a very light oil or baby oil (not WD40) and apply 1 drop at the end of each day for heavy usage, otherwise once or twice a week.
If the characters are not well defined it could be related to one of two factors: the stylus may be set too close resulting in a very shallow mark or if the stylus is too far away the mark may be very deep or the beginning of a character may be missing. With both of these adjust the stylus distance by referring to the instruction manual for power and offset distances.
The second reason may be the condition of the stylus tip. The tip could be chipped or more commonly, it may be blunt and need resharpening. Replace the stylus and/or regrind the old stylus. Contact email@example.com for further assistance.
If the stylus tip has been reground, you may need to adjust the distrance from the top to the marking surface as the stylus will now be slightly shorter