In an electric guitar or bass, it's usually necessary to 'ground' the strings.
By this, I mean that all the strings should have a path to ground — a wire that connects them to a ground point inside the instrument. Usually that ground point will be the back of a pot or the sleeve of the output jack.
When it's properly grounded, you can touch the strings of your guitar and you'll usually hear the background hiss reduce. Yay.
There’s a common misconception that by touching the strings you are grounding the guitar. Actually, it’s the other way around. You see, a human-being actually makes a pretty good antenna. You’re standing there, soaking up electro-magnetic interference without even knowing it. And the guitar is picking some of it up from you. When you touch the strings (or pretty much any exposed metal part on your guitar), it’s you that gets grounded. Most of that EMI that you’re absorbing gets sent off to ground through the guitar and it becomes quieter as a result.
The string-ground is a very important part of an electric instrument and a good spot to start if you’re troubleshooting strange hum problems.
How to ground your guitar's stings
We need to run a wire from one of the common ground points inside the guitar to the metal bridge or tailpiece. Because each of the strings touches the bridge or tailpiece, each one gets grounded.
A Strat is a bit more complicated but here's how not to do it. ;-)
Well, it's certainly effective. It does the job of connecting the bridge to the grounded metal plate around the output jack. 10/10 for grounding effectiveness.
Jury-rigging like this can certainly get you out of a hole if its needed. For something a little more discreet, running a wire into the tremolo cavity and soldering it to the trem-spring will also work. It will have the benefit of not affecting the bridge movement. I'd go for that.