A good tech should do these things before the show:
unload equipment onto stage and into the correct position.
check equipment is working, and sounds 'right'. Loose / dodgy valves, cables and wireless frequencies are common problems.
Ensure guitars are unloaded correctly, checked for travel faults and placed into 'guitar world' ready for maintenance.
Guitar maintenance should be a daily clean of every guitar, change of strings, checking of intonation, new batteries into wireless and ear packs, demarkation of guitars to that night's setlist.
Safely storing all the hardcases, flight cases and other boxes for the loadout.
Check your supplies - are you low on anything?
Ask the tour manager or promoter to get you the things you're gonna need in a few days. Don't wait until you're on your last pack of strings.
Finally start up the guitar rig and get the right tone for soundcheck. In some cases, the techs will soundcheck for the artist - so be ready to know what your guy(s) wants in his monitors.
During the show you should be watching and listening. If there's a bad string, replace the guitar between songs (or asap). Same goes for breaking a string. Listen out of pedal connections (or batteries dying in pedals).
How does the amp sound? And the stage mix?.. You're essentially another set of ears on stage making sure that things are right so the artist just has to concentrate on playing.
Things you should carry depend on the complexity of the setup and size of stage, but generally a flight case or workbox should have:
Enough strings, plectrums, batteries (9V, AA, AAA), earplugs, tape (electrical, stage, duct), spare IEC, spare 1/4" cables (long and patch), spare speaker cables, a few torches, a worktool (like a leatherman / gerber), a few offstage tuners, valves to do the dates you're booked to do.
You could add in a multimeter, cable tester and soldering iron if you're on a long tour for replacing amps / pickups etc.
My tips:
Make yourself be there, but invisible to the audience.
Listen and comment on the stage, but don't intrude on the sound guys.
Be approachable, likable and most importantly - treat him the way you'd want to be treated.
[I'm ignoring talking about drinking, smoking weed and 'partying' with the band - because that can change with bands. FWIW I rarely do it because I'm being paid to be a professional so I don't expect to live the high life. Also, working 18 hour days back to back means it's pretty tough to get hammered every night and be that professional.]
It's a great job if you can do it - and on big tours, it's really fun. Don't get too caught up on things that go wrong just get it fixed ASAP and things should be all cool.
