Okay, we need to take a few steps back here and get the whole picture.

What do you have right now? A stereo mix of 2 channels, left and right? How were those 2 channels achieved?

A) Did a whole band play a live song through a mixer and it was mixed down to a 2 channel tape recorder?

B) Did various players and singers all do their tracks into a multi track system?

Depending on which of those 2 questions gets the "yes" answer, our answer to you will be different, and here's why.

If you have a "master" recording, master in this case meaning "the foundation tracks" and not to be confused with "mastering", then you have some file or tape with X number of individual, discreet tracks on it. Kick on one, snare on another, hat on another and so forth. In that case, each track can be equalized individually to take out any offensive overdriving, noise... in addition, if that is what you have, if a guitar was out of tune or a harmony was flat, you can also go back and record it again.

If you have a file or tape that was mixed as you played and recorded onto L and R channels, if those initial recordings are not clean, overdriven, dirty with background noise, out of tune at all..... It is what it is and there isn't much you can do about it.

There is an old saying that has been attributed to several old school music producers that says "You can't polish a turd", which essentially means "You can't make a silk purse form a sow's ear", or "garbage in garbage out". Whichever of those you choose, it is true. If your baseline tracks are bad, no amount of tweaking is going to fix them and your time is probably better spent recording them again. Not one person on these forums has done everything in one take, and I would say that the true pros of the bunch never SETTLE for one take. Much to be said for the attitude of "Let me try one more because maybe there is a magic moment I missed."

So, fill us in on what you are trying to make sound good. It is FAR from being as simple as using effects. The main thing is to not get frustrated, to not look for the easy way, and to make sure you learn something from every attempt. If it's as simple as "Okay, when I turn this knob, it sounds like crap, so I shouldn't turn that knob", that is progress.