Popular sessions will fill pretty rapidly. On Thursday, you can register for Thursday evening and all of Friday. Saturday sessions are available from Friday morning. The whole kit and caboodle is available from Saturday morning. When they get around to signing up, they find there is no room in their first or second choice.
Veterans go to sign-up first, and then figure things out later.
I have given advice before on how to select sessions, but here's a summary. Fewer people is good. Go for some unexpected things. Pay attention to the Davos bush telegraph. If people are buzzing about a person, make sure you see him or her.