My first personal go-to script is one that has helped me out a lot over the years. Because I have used it a lot to identify missing indexes. I know there are a few different versions available online that you can use. However, I tend to use the one that comes with Glenn Berry’s Diagnostic Queries.
It is so easy to use. I’m not sharing the snippet of code on here because I want to encourage people to download the entire diagnostic script instead. Just download the script that is relevant for your version of SQL Server and search for ‘Missing indexes’.
Read the whole thing.