well unfortunately my job (music producer) doesn't really have any life changing secrets but of course we have some tricks...
Most of you will know about autotune and other pitch correction programs, which can make a pretty frikkin bad singer sound decent if you can be bothered putting in the time to do it (there is an auto setting, but a really bad singer means you basically have to manually put in the notes they should be singing- a major pain in the arse to get to sound natural so only done to this length on big $$ projects). if you wanna hear it in action check out the before and after l to peter andre and jordan covering "a whole new world" from aladin:
The World Today - Peter Andre and Jordan's duet exposes music industry technology
the other big and easy performance fix for us producers is fixing timing- especially in drums, and replacing/supplimenting the recorded sounds with other, better sounds.
So i could play a song totally out of time, at 3/4 the tempo, hitting pots and pans instead of real drums, and fix it to sound like a perfect performance with groove, feel and sounding like i had carter beaufort's drum kit as opposed to pots and pans. Of course it all takes time but its doable depending on the budget.
I can even take the groove from one song and apply it to another- say i had a funk band but the drummer was really stiff, i could extract the grove template from a james brown song and apply it to his drum track to give it the same feel.
Other than that , a lot of the bass and guitar you hear hasn't ever gone through a real guitar or bass amp, rather through digital simulations for speed and efficiency.
Bands with really big budgets generally have more time in the studio to avoid needing to do this stuff, but its there for anyone to learn and use.