Use it on all metal to metal contacts. This includes tube pins, sockets, all jacks - input, speaker out, effect send and receive, pre out, power amp in, and footswitch. It also cleans and lubricates the inside of pots. Here is where to apply it on a pot:
Technical - Amplifier | TalkBass.com. Don't forget to use it on your instrument. Follow the instructions, shake well, use it sparingly.
Some jacks have shunts in them, switches. They need to be opened with a plug so that the contact opens and the product can penetrate. With heavy oxidation, more than one application and scrubbing (I use an inter-dental brush) may be required. Clean up any extra solution that may have gotten where it doesn't need to be. When done, apply a small amount on the contact and don't wipe, it leaves a protective layer.
The product comes in different formats. I prefer the 100% liquid as opposed to the spray, it is cleaner and wastes less.
Technical - Amplifier | TalkBass.com