Facts or statistics are powerful hook sentences since they give real information about your main idea / topic / theme. They should be accurate, interesting and reliable.

Example

If you are writing an essay supporting the use of school uniforms, you could use this:

“According to a 2020 U.S. Public School Report, the percentage of public schools that required school uniforms jumped 8% in the 2017-18 school year.” 

This information is new to the reader and may encourage them to be more compelled and influenced by your arguments.