I've written a lot about data conversion over the years (click here for a list) but when I'm asked by my clients for advice on their data conversion, two tips always rise to the top:

1. Convert the absolute minimum amount of data possible. Look at all the data you have and ask yourself "If we don't convert this, but still have access to it in spreadsheets, what's the worst that can happen?" Cut, cut, cut. Click here for a great (extreme) example of converting the absolute bare minimum of data.
2. Clean data over time, consistently. I call this "weeding the garden." (Click here to read more.) Simply put, if you're not consistently cleaning your data (i.e., weeding), your system will eventually be overrun by bad data, rendering it near useless. You don't just plant a garden and walk away; you nurture it. The same is true for your database.

If you apply just these two tips can help you get your data to where you want it to be: serving the association's mission.