I keep my PS3 always on the same place, I try to never move it from there. It must be placed at least 5 centimeters away from the wall, but I keep it like 30 centimeters away from it. The furniture is made of wood... I have one of those laptops fans below it, always plugged in.
Before turning it on, I clean the place around it so there's no dust to get into it while I'm playing... (dust will still get inside of it because the air itself carries dust, no way to get rid of that)... and then, I take the cloth I cover it with off the PS3, and clean the dust that's on the PS3 (not much, but there's a little even though it was covered).
Then I just play like normal... but when I'm about to turn it off, I exit the game and take it out of the console, then I keep the PS3 on for around 15 minutes doing nothing so the fans keep working and the PS3 cools down a little before turning it completely off. Then I turn it off and unplug it, and wait for around 30 minutes to give time to the heat that was inside of it to leave and then cover it again with the cloth completely without giving dust any space to get in the console.









