Cleaning a Computer
Starting at the top and working down:
First making sure the computer is turned off otherwise all sorts of strange things are likely to happen.
To clean your screen use a soft damp cloth, or a very small amount of a mild window cleaner sprayed onto a soft cloth. You do not need to buy expensive screen cleaners but you should be careful not to scratch the screen or use anything that might melt the plastic.
To clean your mouse and keyboard, use a damp cloth. Things tend to get down between the keys of the keyboard like bits of fluff and paper you may need to use compressed air to get this out, this can be bought in cans from most supermarkets or computer shops or use a small compressor with an airgun attachment (being very careful as this type of air is extremely powerful and can also be slightly damp).
To clean your computer or laptop, wipe over all the surfaces including the fan vents at the back and the front with a damp cloth this should remove most of the dust that’s caught in the fan vents. You may need to use compressed air to blow through the fans, the heatsinks, and vents. To access these parts you might need to open the side of the computer, it's often a good idea to unplugs the computer and take it outside before you blow it through, computers collect huge amount of dust inside and you don't want this all over the living room. You should also be careful to hold the fans as you do not want them spinning around at high speed while you squirt the air, as this could damage the computer. If you cannot hold the fan then use a folded piece of paper and carefully push it into the fan.
Keeping your computer clean and dust free will help to keep it cool, will reduce the risk of it crashing and will generally extend its life.