I take care of my stuff. I insert connectors carefully. I will sit and untangle cables and gently straighten out coiled cables. I use good batteries, which I manage charging for. I don't drop them. I always use a wriststrap if available. I don't open them up if I can possibly help it. If I do use "unofficial" addons like chargers, PSU's, lights, etc. then I check them carefully before using (usually with a multimeter) and "lock" them to the right settings (bit of sticky-tape over the voltage switch etc.). I do my best to protect the screen but don't believe in screen protectors (I've seen them destroy Palm touchscreens because they "solidify" the screen a bit more and so pressure on the upper layer causes pressure on all sides, which ultimately breaks the screen entirely - you don't get marks on the screen but one day it will just refuse to calibrate).
For my previous handhelds, I had large, hard cases that I could fit everything in (e.g. console, carts, link-cables batteries, charger, headphones etc.). My original Gameboy I sold on eBay in 2005 (15 years after it came out?) still with all the original parts, instruction manuals, games, chargers and accessories (not boxes, though, because I put it in a case). My original Game Gear I sold in a similar situation, with TV Tuner and all the games in a hard case - the only thing "wrong" was the original PSU's cable had worn out through years of being plugged in and so the cable had broken inside the wallplug. I had to dismantle it, repair it, and tape it back together. Oh, and I think the TV-Tuner aerial was a wee bit smaller than it started out as because it was such a vulnerable part.
For my GP2X, I keep it in its velvet bag with a little spectacle-cleaning cloth for the screen. I only put it down in safe places (and, because I love it so much, always mention to the wife where I have put it down so it doesn't get buried). I try to not put pressure on the joystick when I store it (because that looks like a vulnerable bit to me). I'm very wary of the little rubber port covers and the fact that the PSU connector is so flimsy. I'm hoping to get 10 or 15 years use out of it, so I can show it to my (minus two weeks old) kid.
Strangely, I probably played with my consoles more than most people ever do. When I bought my second-hand GP2X, it came from someone who'd had it years - it had the Value Pack, two homebrew games that didn't work and a couple of MP3's on it. They can't have used it at all. Every single electronic gadget I've owned got played to absolute death. We once worked out that my original 48k speccy had tens of thousands of hours of play (we only broke it twice - both times on the same game - Daley Thompson's Decathlon, which requires lots of joystick wiggling and broke our Interface 2 port twice - it was only a "resolder" job, though and my dad fixed it). I was bought an electronic boxing game when I was about 5. I still have it. It's got a set of red LED's for the "screen", two joysticks and two buttons for each player - it still works perfectly and it was played on and off for hundreds of hours over two decades.
My friends manage to break just about everything known to man. I would never lend out my consoles at all. I was wary of even lending out games. I no longer lend out CD, DVD's because they ALWAYS come back scratched - I'm so careful with other people's discs and would even clean them if they were grubby but nobody else bothers when its my discs!
Basically - watch what you're doing. Don't balance them on the edges of chairs. Remind yourself how much they cost and what a hassle it would be if they were to break. When you put them down, think about where you've put them and what's "vulnerable" on them.
My GP2X has taken one dive in the year I've had it - it was in my coat pocket, and the hook the coat was on fell off the wall entirely. It hit the floor and "popped" the casing open. I was heartbroken. I carefully popped the two halves back together and turned it back on in trepidation and fortunately all was well - not even a scratch because the coat protected it.
Paulo Becker said:
One thing I do (though I have no idea if it really helps or not) is always put those silica-packs inside the protective case along with the videogame to prevent moisture and humidity from acting up.
I'm not sure that helps any unless you are in a humid atmosphere or see signs of condensation etc. I've never bothered with those packets and never seen a single sign of corrosion on anything that I've kept stored away indoors.