Newbie stuff here, but I figure this may be helpful for anyone looking to do this stuff. Here's the quick and dirty on automating. For this uber-howto, I'm going to automate panning. Note that at least in this case, panning is much easier to do on a control surface than with a mouse.
So here's my project, which has two lead lines. One called "Lead Low" which I use as my usual up-the-middle lead, and another called "Lead High" which is my harmony track when I want to get all Maiden and harmonize.
Lead Low already has an automation curve on it, so here's how I'll do it for the Lead High track.
What I'm doing here: When when harmony comes in, I'm panning the Lead Low track all the way to the left, and panning Lead High all the way right at the same time, and then bringing them both back center at the end of that particular section.
(Note: Actually panning both 100% does not sound good, haha).
So select your track, and hit P to bring up the Pan envelope. (Right click the track > Envelopes > Pick the Envelope you want to automate.) Once you have the envelope selected, right click the envelope track and set the track automation mode to Write.
Then arm the automation track. You'll see the selected thing you're automating turn red.
Then just play the track, and adjust your pan/fades/etc accordingly. You'll see it create the automation curve as it plays, and you can (duh) edit it afterwards to make it smoother/delete points, etc.
Then just make sure you disarm the automation track as soon as you're done.
And that's it.
And here's an automation curve done manually w/o recording it in Write mode, which is a lot cleaner with a mouse. Stuff like fading as you mix will obviously be better doing it while playing the track, and again a little outboard control surface like the Korg Nanocontrol (like $60 on Amazon) makes it much easier.
Just remember to add a start point for your automation that's at zero (center in this case), because if you make your first control point actually do something, it will effect the rest of the track before it. So in this pic, I have a start point at the beginning of the curve, a start point at my maximum pan, an end point for the maximum pan, and then an end point so that the curve is nice and smooth coming back to center.
This is a great way to add a little snazz to mixes. And hey, who doesn't like snazz?