Guitar volume and tone knobs let you control the sound and levels of your guitar without running over to the amp. When one of the knobs falls off, it not only looks bad, but it makes adjusting your guitar much more of a hassle. Reattaching or fixing a guitar knob is pretty simple, it just takes a little patience and some know-how.
Determine what kind of guitar knobs are on your guitar. A knob for a solid shaft pot will have a small hole in the side where a screw is sometimes used. A press fit guitar knob (common on Stratocaster-type guitars) won't have a small hole or a screw in the side. Spin your guitar knobs around and look for the small opening.
If your guitar knob is loose and tends to fall off, tighten it up. Use a nickel coin or similar object, place it between the two halves, and gently separate them until the knob stays in place. If you have the other type of guitar knobs, use a small hex screw or flathead screwdriver to tighten up the knob.
If tightening up the knob doesn't fix the problem, you need to take off the guitar knobs. The FretNotGuitarRepair website suggests using a thin rag to gain leverage on press fit guitar knobs. If you have solid shaft knobs, use the screwdriver to unscrew the knobs and then gently pull them off.
Try to determine the problem from the exterior of the guitar. A loose knob may be the result of a worn-down groove around the area of the shaft the knob attaches to (if you have solid shaft knobs). If this is the case, reattach the knob a little higher up on the shaft.
Unscrew the plate housing the electronics on the back of the guitar. Check to make sure the wires are all attached so the knob is effectively changing the tone or volume of the guitar. A loose wire or broken connection can stop your knobs from functioning properly. If you see a loose wire, solder it to where it was previously attached.
If the problem is beyond a loose wire, take your guitar to the professionals; it's probably a wiring problem best suited to be handled by a professional guitar luthier. Take your guitar to the local guitar shop.
Use something that won't damage the finish of the guitar for press fit knobs. A small rag works well, but a thick guitar pick might also do the job.
Avoid using a screw driver or metal tool to gain leverage on press fit guitar knobs. This could damage the finish of the guitar. Don't solder the wires in the back of your guitar unless you can see where the wire was previously attached.