D5 on interconnect connectors, speaker cables, and the 3 prongs on a power cable. And the connections on the components. Using a soft cloth, I clean the RCA jacks, XLR pins, speaker and amp binding posts.
I've never used a liquid on AC receptacles. Pulling the cable termination in and out to possibly better the contact is good enough for me.
Also, when I buy a tube, NOS or used, I let the pins sit in a bath of D5 liquid for about 15 minutes. Just enough liquid to cover the pins.