I use compressed non-flammable canned air for getting the dust loose and, depending on the location and weather, let either the wind blow the dust away or use a vacuum cleaner. In the latter case, I don't put the nozzle near circuit boards to avoid static electric shocks. If the fans are heavily covered with dust on the cooler side, I unscrew them apart from the cooler and either blow or brush the dust away. There's usually a sticker on the other side of the fan, under which you can find the bearing, sometimes covered with a rubber plug. Just one drop of sewing machine oil (motor oil will do) will lengthen the fan's life. WD40 or similar products won't do, they are too thin and will clean all lubricant out, making things worse. Taking the video card out for maintenance is a good idea, the fins get easily clogged and there's not much room around the fan. Taking the fan apart for cleaning and lubricating from a vidcard is IMHO even more important than in other parts of the computer, having seen too many of them burned after the fan has finally stopped making that grinding noise... While at it, why not clean the card's contactors with a rubber. Same can be done to memory sticks.