En Passant made this document in October of 2018, and it has been moved here for organizational purposes. It describes Everything You Need To Know About SA2 Speedruns, including detailed descriptions about many skips and strategies. Some information may be a bit out of date at time of posting but almost all of it will be relevant forever.

https://docs.google.com/document/d/1YB_IyAjwTxTHKdXkCZ4nmaZQyp1NvwBEKfehFBIY7R0