A basic but important aspect of configuring Live is the Exclusive setting (located in the Record/Warp/Launch tab of the Preferences screen) and how it’s modified by the Command or Ctrl key.
When turned on, this option prevents multiple tracks from being Soloed, or Armed for recording simultaneously. Beyond that basic fact, the important thing to be aware of is that the Command (Mac) or Ctrl (PC) key is used to reverse the current exclusive behavior.
I keep my Exclusive preferences set up as seen above.
Arm exclusive is on – I find that it’s really easy to accidentally leave tracks armed for recording which can lead to some very aggrivating unintentional recording. I rarely record on more than one track at a time, so this works well. To arm multiple tracks simultaneously, I’ll just hold down the Command key while clicking the Arm switch.
Solo exclusive is off – I solo multiple tracks all the time, so this is the most convenient for me.
In this case, holding down Command makes the Solo switch behave as if Exclusive were turned on. This is particularly handy when you’ve soloed a number of tracks and you want to un-solo them all simultaneously. Just hold down Command while unsoloing any one of the tracks and the rest will follow suit.