Most people go on several job interviews, get a job and that's it. But with side musicians, every job is an interview. Generally we are hired one gig at a time. If it doesn't go well we may not get a call back.
There are many things you can do to make sure you "get the gig" or keep the gig...
1. Be on time - I like to be early
2. Have gear/guitars all in good working order - problems happen, but strangely more often to those who don't do the prep work.
3. Turn off the phone - or at least mute it.
4. Know the music - if it's a gig that they get you mp3's beforehand - it's for a reason.
5. Have a pencil handy - make note of changes so you don't have to ask twice.
6. Be flexible - if they want you to use a different guitar or their amp... cool.
7. Be a good hang - No one wants to spend 16 hours cooped up in a studio with a jerk.
8. Access the tempo of the gig - is this "music by pound"? Or "let's try seven more amps"?
I like to think of each gig, session, lesson as an opportunity to get the next one. The people you work for will appreciate this attitude.
I remember hearing great drummer Gregg Bissonette talk about his audition for David Lee Roth. He was waiting in a cattle call situation for his turn. Several drummers were before him. One dejected drummer emerged from the audition.
"How was it?" Gregg asked.
"Man there were some crazy time signatures, 3/4 to 7/8 to 4/4 to 7/8..."
So Gregg got out his Sharpie so he could make notes on his snare head.
The next guy came out complaining that they had a double kick and he sucked at double kick. Gregg immediately started warming up his feet and calves, practicing his double-kick.
Another drummer said they were looking for a heavy hitter. He admitted his jazz chops were not going to cut it. Gregg got out his heaviest sticks. When he sat down at the set with Steve Vai and Billy Sheehan the first thing he did was hit his snare really hard making Steve practically jump out of his skin. Then Steve turned to unknown young Bissonette and smiled. He got the gig.
So I guess another tip would be...
9. Pay attention
David Lee Roth - Eat Em & Smile
David Lee Roth - Skyscraper