#1
I am a guitarist so I have no problems with this but just so I can help others when they come to me:

What do you do as a pure singer/rapper (ie no instruments at all) during a solo or the like?
Theory is just...wow. I'm getting a bit over my head by trying to learn so much w/o formal educators

Quote by DBKGUITAR
To be a good lead guitar you must be VERY GOOD AT RYTHM

Quote by MaggaraMarine
My motto: Play what the song needs you to play!
#2
Just get into the music. Look at vids of your favourite bands to see what they do.
And no, Guitar Hero will not help. Even on expert. Really.
Soundcloud
#3
The members of Zeppelin used to leave the stage during John Bonham's solo in Moby Dick, so that's an option if you're playing a 1/2 hour solo

Otherwise clapping out the beat, working the crowd, interacting with other members on stage or taking a break to drink a little water are all great options.
#4
Beatbox.

Seriously... I just step aside and clear the way between the audience and the soloist.

CT
Could I get some more talent in the monitors, please?

I know it sounds crazy, but try to learn to inhale your voice. www.thebelcantotechnique.com

Chris is the king of relating music things to other objects in real life.
#5
Sammy Hagar used to go backstage and get blowjobs from the women that would come back there during the long solos that Eddie Van Halen would perform as part of Eruption.

There is nothing I dislike more than the vocalist yelling and shouting stupid stuff like "lemme hear ya!!!" during instrumental sections. I happen to like a lot of those interludes and don't want to listen to "yeahhhhh" and other stupidity. Just go away and come back later.