For the past 2 days, I've been rearranging the storage areas here at Astronomy magazine. It was lots of work and lots of fun at the same time. And, it got me thinking. Why do some telescopes last 5 years while others last 50? The answer, it turns out, boils down to one word: dust.
If you can protect your telescope from dust, it will last a lifetime. Now, I'm not considering killing forces like water damage and blunt-force trauma. Those can end the useful lives of any type of equipment. But even a well-cared-for telescope will deteriorate if left to the ravages of dust.
Most obviously, dust coats optics. A thin coat won't affect your views much, but as months go by and dust builds up on lenses and mirrors, star images look less like stars and more like something you'd see on the Fourth of July.
Dust also affects bearings, drive motors, and electronics, not to mention a telescope's finish. Dust in your go-to drive's lubricant results in less accuracy finding those faint fuzzies.
At this point, I could go through a short lesson in cleaning telescope optics, but, first of all, that's no fun; and second, most amateurs fear cleaning their optics more than meeting a cougar at a dark-sky site.
All that's left, then, is prevention. Don't let dust accumulate in the first place, and you won't have to deal with it later. Cover all openings and exposed optics. Don't leave eyepieces out. Replace their protective plastic caps, and put them back in their boxes. Dust won't overcome a double level of protection like that easily.
For refractors and catadioptrics, replace the front aperture covers. If the cover fits loosely, or if you notice even a slight dust build-up, add a "shower cap" cover of fabric or plastic that will add an extra layer of security.
If you own a Newtonian reflector, be sure to cover both the front and back of the tube. For all telescopes, don't forget to seal the focuser hole. The easiest way is with an inexpensive eyepiece.
For long-term storage (more than 6 months), I strongly recommend you double-box your telescope. This technique works well enough that you can store your scope in a waterproof garage. Place any accessories in sealable plastic bags in a sealable plastic box.
Hey, you can't be too careful. This way, when you're ready to use your telescope again, you won't have to turn into a restoration expert.