How to properly play a seven-string?

[Konfyouzd]

Don't force using the 7th string. I only recently started using it more in riffs and usually it's to hit a chord that I could hit on the 6th string, but it's simply quicker and/or more convenient to use the 7th string instead.

For instance if I were doing some quick down picking riffing and I had to go from an A to an F it'd be easier to hit the F at the 6th fret of the 7th string [for me].

 

[Alberto7]

^ Agreed.

I've had my 7-string for over a year and a half now, and I don't use the 7th string as often as one might think. For metal, I use it mostly to learn Dream Theater songs I often use it to complement chords by adding a lower frequency that might make the music sound a little richer.

However, I don't do much metal with the 7th string. At least, not original music that could be classified as metal.

Other than that, I use it a lot for jazz. It's really good to use when "walking the bass." For example: When playing a maj7 chord with its root on the 6th string, it's much easier and more convenient to play the perfect 5th of that chord on the same fret as the root, but on the 7th string, than having to go down 5 frets on the 6th string to play it.

Picture a Cmaj7 chord (or just a plain major or minor chord... It doesn't matter which one for the purposes of this example), with its root being C on the 6th string (8th fret being held by my index finger). Now, if I want to hold that Cmaj7 chord, but I want to add a lower perfect 5th to "walk the bass" a little bit, I can just easily and comfortably get my index finger (which was holding the 8th fret on the 6th string), and move it to G on the 8th fret of the 7th string... Rather than going all the way down to G on the 3rd fret of the 6th string.

TL;DR: Unless you want to chug away on low notes (there's nothing wrong with that), it's just a matter of convenience to have a 7th, low B string. It can also make your chords sound a bit fuller occasionally.