Rule No. 1 for enjoyable computing is the computer always wins. All electrical devices generate heat, which is why computers include internal fans or have cases designed to boost air flow. Heat is an enemy because it causes things to expand or to respond differently to electricity. If the printed circuits on your computer's motherboard and peripheral cards are too warm, they might make or break electrical connections. The usual symptom is the computer working perfectly for a short time after start-up, then becoming cranky and eventually comatose.
Dust is everywhere.
When it filters into the vents of a computer, it settles on components, building up insulation until the components don't release heat as fast as they were designed to do. Keep your computer in a relatively dust-free area. Be diligent about dusting behind and beside the machine. Be sure to get rid of any pet fur, which is an even better insulator than dust. Never spray a cleaner onto or around the computer's keyboard, vents, fans or drives.