Choose XML format.
Download at least one month of data. More data is fine but data older than a month won't be included in the analysis. If you have less than a month's worth of data the analysis won't work.
The data must be recorded at least hourly. This usually isn't an issue since hourly is the default for most Green Button downloads.
The data must be for a residence. Apartments, condos or townhouses are fine, but data from commercial buildings will not produce accurate results.