Yesterday I had 2 day 2s and while sitting on public transit to meet the first one I realized I've developed a ritual for pumping my state before I go out. I wish I knew this when I was new, so noobs take notes here.
Step 1 - days before
Eat well. Seriously, I know it's corny, but if you normally eat lots of junk food and do lots of drugs, this is gold. A good diet will improve your mood. So can working out.
Step 2 - Same day
I put on music that gets me pumped and ready to go. Everyone has music like that, I won't pretend to know what songs work best for you. The trick though is to actively listen. Don't just ignore it, but get dancing in your seat. Get moving, singing, smiling, whatever effect it has on you.
I also put on tons of comedy acts, particularly improv comedy because when you really focus on it, you will get more into the 'zone' of dropping inhibitions and getting out of your head.
Step 3 - In the venue
This is awesome if you take a bus or train. Watch the people around you and start riffing them in your head. Try to come up with some funny shit they *might* be thinking. For example
<old guy is reading a newspaper>
"Ok, you can do this. What does the letter 'a' sound like? Uh... I dunno..."
<crosses arms suddenly>
"Fark yeah, I remember! A says 'ah'!"
<a solid 10 with perfect everything walks past>
"omg I'm ugly, that freckle has ruined my life. Maybe if I get a power sander I can remove it. Then psychoactive will want to do me, right? Oh no, did I remember to throw up today?"
and so on. As a naturally introverted guy myself, this routine gets me out of my shell and suddenly I can talk to anyone because I've gotten into the swing of coming up with something 'on the fly' and after a bit of practice it gets funnier and funnier.