Change management for all of your custom objects
If I could go back in time and counsel my clients on one thing they should do differently in their implementations, it would be to do a better job of managing (and limiting) the changes they make in their account. NetSuite's amazing flexibility is great up to a point, but you know you've overdone things when users start to complain that they can never find the fields they need to set values in, or when nobody knows what a set of fields on a screen is used for, if they are used at all.
It's for these reasons and more that developing a solid, workable change management plan is such an important part of every NetSuite implementation. This process can be very simple or much more formal and complicated, depending on what the business wants and needs. I have worked with clients who were small enough that we just wrote up a single Microsoft Word document, describing all the custom configuration and automation we created...