What is your unit of analysis?

• Microdata – individual level 
• Macro/Aggregated – country, region, etc.
• Survey – one-off, longitudinal
• Time-series – variables over time
• Geospatial – geographical co-ordinates
• Text—emails, tweets, articles

See if the dataset or database provide a citation

Citation Guides:

Objective:

• Complete:  how many missing values?  Sample size?
• Documented:  Are the variables defined? Clear methodology?
• Format:  proprietary format, software?
• Is the format and variables consistent over time?
• Flexibility:  can it be used with other data?

Subjective:

• What is the repuation of the source? Do you know the publisher?
• Is vendor support available? Look for documentation
• Is this cited in top journals?
• Is the source used by peers institutions/known researchers?