I'll agree PARTLY with that last post. Accumulated dust certainly can cause problems and should be removed carefully. However, a compressed air hose at a garage is not really a careful method. First of all, such air normally has some moisture and oil droplets in it that can spray out at unpredictable times and contaminate your system. Secondly, the pressure usually is high enough that you MIGHT loosen something. Thirdly, sometimes very high air flow rates over components of your system can generate static electric charges that can result in small discharges through things that can damage them. If you're going to use compressed air, the preferred method is to buy a can (or several) of CLEAN compressed air that is designed for this purpose. It also has low pressure and is unlikely to cause static electricity problems. I know, that's a lot more expensive.
I have a cheaper method which I think is gentle and safe, although others may disagree. It involves using a common household vacuum, which many tell you NOT to do because it CAN cause static electric charges and damage due to high air flow rates and contact between the vacuum hose and the mobo. To avoid those hazards, I do NOT bring the hose close to components. The resulting low air flow is not good enough to loosen some of the dust. So I use a plain dry clean artist's paint brush and carefully brush over all the places where dust might be, holding the vacuum hose in the near vicinity. The dust loosened by the brush floats into the air and most gets swept away by the suction of the hose.