No matter the subject statistics are limited by both time frame and geography.
Time: Are you looking for information about a single point in time? Do you want to look at changes over time? Do you need historical information? Current information?
Be prepared that the most current statistics may actually be a year or more old! There can be multiple year lags before some information is released depending on how often the information is collected, the time it takes to process and crunch numbers, and the public release schedule.
Geography: Geographical areas can be defined by political boundaries (nations, states, counties, cities) or statistical boundaries (mainly Census geography such as metropolitian statistical areas, block groups, or tracts).
Remember to define your topic with enough flexibility to adapt to available information!
Start by defining your topic
Be specific about your topic so that you can narrow your search, but be flexible enough to tailor your needs to existing sources.
Identify the Unit of Analysis
This is what you should be able to define:
#1 - Who or What?
Social Unit: This is the population that you want to study.
It can be...
#2 - When?
Time: This is the period of time you want to study.
Things to think about...
#3 - Where?
Space: Geography or place.
There are two main types of geographic classifications...
Remember to define your topic with enough flexibility to adapt to available data!
Data is not available for every thinkable topic. Some data is hidden (behind a pay-wall for example), uncollected, unavailable. Be prepared to try alternative data.