HowToCleanEdgeConnectors

• Observe anti-static precautions
• Don't set fire to yourself
• Don't blame me if you break stuff
• Wear suitable gloves, avoid inhaling solvents, use appropriate ventilation etc.
• Clean edge-connectors with a cotton-bud (cue-tip) dipped in isopropyl alcohol ("IPA"/Isopropanol)
• Clean DIMM/PCI slots using a stiff piece of card (the same thickness at the DIMM/PCI PCB), wetted with isopropyl

Isopropanol is available from many chemists/pharmacists.

You can also buy commercial connector, and PCB cleaning solutions and devices.