This depends greatly on the individual and the thickness or coarseness of the hair. Some prefer to change a blade after using it once or twice, others after 3 or 4 times while many expect between 5 to 7 uses. The key is to change it regularly and always use a sharp blade. The more blades passing over the skin per stroke means a faster and smoother shave and less irritation or razor burn for sensitive skin. So depending on the density of hair growth, select either a single, double or triple head shaver.
Some electric shavers are dry shavers so no gels or lotions are needed in preparation.
A pre-shave lotion is recommended though by many. Others are wet shavers requiring gels or lotions to be applied first and some other shavers can be used either wet or dry. Two or three weeks may be needed before good results are seen as the skin needs to adjust to a new shaver. At least three weeks are needed if changing from a blade. Every time a blade is used, a tiny layer of skin is removed.