Based on my experience, I substantially agree with what’s already been said; my top mistakes would be as follows:
* Getting too invested in a deal and wanting to win, even when economics no longer support continuing
* Insufficient communication (especially where time zone / language barriers exist)
* Overly optimistic perceptions of synergies, or synergies that were generated to justify the deal rather than what was realistic
* Overly aggressive timelines on realization of said synergies
* Insufficient planning/resourcing dedicated to post-merger integration activities
