I'm going to replace my antenna and wanted to clean my N connector well replacing the antenna. What's a good way to clean it?
You can use some electrical contact cleaner, but be careful. Don't use lots of it and you don't want it getting down inside the cable.
Follow up with some compressed air (carefully) to make sure it's dried out inside before reconnecting.
If it's a silver plated connector, you'd probably need to remove the tarnish, but that's going to be difficult. If there is any questions, do as ko6jw says, and just replace it. If it's really nasty, water could have got inside and damaged the coaxial cable.