Look for facts, i.e., something you can verify. Statistics and other numbers can be good because they are easy to compare (for example, crime rates from one source are easy to compare to crime rates from a different source).
Be careful that the statistic you're using is actually about the exact thing you're talking about [here's an example]
Ignore rhetoric [using language effectively to please or persuade]
Ignore images; they're too emotionally manipulative