Here's a summary of what we have learned and tell people we train. Always keep dust caps on connectors, bulkhead splices, patch panels or anything else that is going to have a connection made with it. Use lint free pads and isoproply alcohol to clean the connectors. Cotton swabs and cloth leave threads behind. Some optical cleaners leave residues.
Residues usually attract dirt and make it stick.
We have been supplying Texwipes Alco Pads for over 10 years with every Fotec Test Kit with no problems. Years ago, you could buy a can of plain dry nitrogen to blow things out with, but it's long gone. A better way to clean these bulkheads is to remove both connectors and clena with Alco Pads, then use a swab made of the same material with alcohol on it to clean out the bulkhead. Detectors on FO power meters should also be cleaned with the AlcoPads occasionally to remove dirt. Take the connector adapter off and wipe the surface, then air dry.