There are a few things that can “kill” your camera equipment, both in function and value…
The first “killer” is DUST. While keeping your camera & lenses away from dirt & grime sounds like common sense, it’s not always the case. Even if you avoid specifically dusty areas, it is inevitable that dust will still creep in to every crevasse it can. The most important part to keep dust out of is your digital cameras sensor. Some ways to prevent this (as much as possible) are: If there’s no lens on your D-SLR, it better have a body cap on it! Always keep the internal parts of your camera protected. It’s best when changing lenses to do it when the camera is off, and to hold the mount slightly downward as you’re changing. Also, if your other pieces of equipment are dusty (like your lens) it can easily transfer to your image sensor. So, also keep everything as dirt & dust free as possible.
You can purchase compressed air cans which give a nice swift blow of air onto whatever you’re pointing it at. There are also bulb blowers which are easier to transport in a camera bag, are inexpensive, and are an easy way to keep those nasty little particles away.
In addition to keeping your equipment properly stored, I suggest silica packs. These can be purchased in large sizes that can be re-activated by cooking it in the oven (best for larger spaces or multiple pieces of equipment), or for a temporary (& smaller space), the little packs that come in shoe boxes can be thrown into your camera bag as well. I also use these in my print boxes for preserving old photographs.