I have a digital SLR and when I look through the viewfinder, I have to remind myself to keep my nose away from the LCD screen, otherwise, it suffers from the odd smear or two and I do seem to be always cleaning it. No, not my nose, the screen! There are, however, clear adhesive screen protectors you can purchase to remedy that and they will also guard against scratches, etc. Now I can well imagine how dirty my lens would also get if I didn't keep my lens cap on. So, the first tip would be to ensure you keep it on, whenever the camera is not in use. And keep a lens cleaning cloth (or pen) in your kit at all times, but only the ones that are made especially for that purpose and change it regularly. Available form all good camera stores.
If you have an SLR, to protect your camera lens, it is advisable to fit a screw-on UV, or skylight filter and keep it on at all times. Excepting, of course, the times when you need to use a different filter. It is cheaper to replace the filter than to be up for the cost of a new lens for the camera. And don't screw other filters directly on top, as it may increase your chances of getting lens flare if you are shooting towards the light.
As you change lenses it is very important that you do it as quickly as possible, so as not to allow dust particles to infiltrate the interior of your camera. A puffer (or blower-brush) is handy for keeping dust out. Also available at camera stores. However, it is very important that you read your camera instruction manual before attempting this. See my next chapter on 'Camera Cleaning'
The camera usually comes with either a wrist or a shoulder strap. If you have a wrist strap fitted, it is not to be used as a handle or to swing your camera, you slip your hand through the loop and hold your camera that way. Then, if you happen to drop your camera, the looped strap will still be attached to your wrist.
On the other hand, if your camera has a shoulder strap, for safety, you can both carry your camera and take photos at the same time with the strap around your neck. Or, if you are like me and you prefer to hand-hold the camera, at least wind the strap around your wrist two or three times. This will not only provide safety but also allows for a firmer grip on your camera whilst shooting.
If you are travelling, always secure your camera in a vibration-free area and in particular, don't stow in overhead aircraft lockers, as the vibrations can cause damage to sensitive electronic components.
When you go out to take photos and there is the remote possibility that the weather might change and not necessarily for the better, take a plastic bag with you, about the size of a shopping bag, so that you will have some protection at least for your camera. You can even fashion it to cover your camera whilst you are still shooting. Simply stretch it over the lens, then cut a hole in it to allow the lens to poke through. For your own safety, always wear appropriate footwear and clothing. Desperate means provide for desperate measures.
I know I go on about tripods and some people think they have good enough reasons not to bother with them, but they do provide a firm, secure base for your camera (especially in low-light situations) and they do give your hands a little extra freedom to do other things with whilst preparing for the shot.
It is not a good idea, however, to carry the tripod over your shoulder with the camera fitted. I found this out the hard (costly) way. I severely damaged my flash unit, which was fitted to my camera at the time, when it collided with an unnoticed, overhead object. Thereby costing me much grief and not to mention the cost of the repair job.
As you accumulate the odd lens or two and assorted bits and pieces, you might consider purchasing a bag to keep all your gear in one handy place.
There are some very suitable shoulder bags or backpacks on the market designed especially for photographer's needs and they keep all your gear safe and sound.
You should never subject your camera to extreme heat. Extreme cold isn't too bad, but the power in your batteries will suffer.
There are probably many more things we could think of for the safekeeping of our gear, but I think it all just comes down to good old common sense and we should just give a little more thought to the things we are doing when we are doing them.
Whether you own a simple point and shoot camera or a top of the range SLR, you need not only to protect it from the elements, but also from yourself - as I personally have discovered.