I'm far from an expert so don't take this as gospel but...
What I usually do is do a mixdown, and look at the spikes on the waveform and keep a note of where they are in the tune, and go back to the mix...
Then I'll go to say point x, where it spikes, and play the part over and over, muting different things, and watching the levels on the master fader. I have found that a lot of times its like 1 instrument causing it to spike. So then you know its that track thats causing some trouble, possibly in conjunction with other tracks. I have often found that lowering the level of an individual hit can make a lot of difference.
All in all its kind of playing around and seeing what it is thats causing the spike. It could be that one track is fighting with another, in which case some EQing of the conflicting tracks may be in order, or maye some very mild compression. Try solo certain tracks together to see if they are fighting.
Once you have a rough idea of whats causing it, you are well on your way to finding a solution.
Sorry if this post has been pointless
