I made a fortune as a jingle singer in the 80's.

I was the voice for all of the Spuds McKenzie commercials, and Kelloggs Nut and Honey Crunch...
I did many spots for Mconalds and Dominos Pizza and Hasbro and dozens more.

I got the first gig because a producer heard me singing at a gig with my band and thought my voice would be right for an Olympia Beer spot.

I kept the gig by being early for every session, being a quick study ( one or two takes and I was good to go), by listening carefully to what the production team was looking for stylistically, and like Jody said, singing in time. (although, many times producers are looking for someone who can sing away from the rhythm as well)

I lost the gig because I took a bunch of the money I earned and put a recording studio in my house and began producing buy-out spots on my own.

The agencies got wind of it and P{OOF !..my career was over !

So..like Jody sez..sing in tune (or out of tune if that's what they want) and learn to be fast and flexible.

bob