Mistakes that you encounter in crown preparation are mostly irreversible, though some you may mediate or troubleshoot it in a way, but most often when you do this, you are making it all worse. So the better approach in this case is to always take every thing slowly and smartly, do not rush on reducing and cutting away tooth surface. There is nothing wrong if you stop in the middle of the prep just to check if anything is still ok. Also, before starting any reduction, it is always and always a good measure to plan anything ahead. Determine the anatomy that may influence your prep and set forth a clear objective of what your prep will appear before reducing that surface.