Looking at that circuit, it appears the sleeve is missing on the output and input jacks. All jacks have ring, tip and sleeve. usually tip is hot audio, ring is cold return and sleeve is ground. So audio cables are wired tip=red, ring=black, sleeve=screen of cable - if that's your cable.
XLR connectors (large 3 pin plugs) stand for X=screen, L=live(hot), R=return.
So when we plug everything in we hope we don't get HUM.
I would not use the battery switch on input jack connector - use a separate on/off switch - likely to get great splats plugging in jack.
On that circuit the sleeves(long bit) goes to common ground(earth like symbol) also the other three points Q1, 47k resistor and 2k pot. If you use a switch for battery then the + battery goes to one side of switch, the ground the other.
On the subject of earths, in a TV studio for instance, it may have a power earth - all the lighting and 3 phase supply. Technical earth would be the racks and equipment, domestic earth all kettles, microwave, watermachines, air-cons etc. So when someone plugs the kettle in it dosn't take out the Studio.
I just forgot on thing you may have to connect ring bit to ground this depends how guitar wired.
Happy fuzz sound!