How good have you been, how well do you recruit, and whom do you return? These three questions are the building blocks for how we set expectations for a college football team in a given year, and they are how I go about putting together preseason projections for my SP+ ratings.
Here's how I address each question:
How good have you been? For this, I look at a weighted average of recent performances. Yes, last year's SP+ ratings are heavily involved, but adding in your ratings from previous seasons with diminishing weight (so what happened five years ago doesn't matter nearly as much as last year) gives us a pretty solid way to measure overall program health.