When not in use, keep the optical surfaces covered against dust accumulation. You should check the primary and secondary mirror surfaces periodically to make certain their coatings are not tarnishing. Do not observe under high- humidity conditions because this can leave a coating of moisture on the mirrors. If the surfaces get damp, you need to clean them immediately with lens tissue or some other soft, absorbent and lint-free material. Be careful not to apply too much pressure to avoid scratching the surfaces. Never tough the reflective surfaces with your fingers because the oil on your skin is highly reactive with the coatings. Fingerprints can be removed by swabbing the area with denatured alcohol with a cotton ball.
With proper care, a reflector should last 5-10 years or longer if the mirror 'slivering' or 'aluminization' is of high quality, and you have been careful about moisture and dust.