Not many people know what made the Dead different. Both Jerry Garcia and Bob Weir wrote sings, and had covers they liked to do. They'd have something resembling a playlist for the first set, but rarely knew when they started more than what two songs they'd start with.
The end of each song would devolve into an improv jam, and Garcia, Weir, and whichever keyboard artist hadn't drunk himself to death yet would then add licks if whatever they wanted to play next. They rarely just bridged to the next song, they were usually trying to bridge to at least two different songs.
Phil Lesh decided which song was next. Every time. It's rock and roll, and where the bass guitar goes, the band goes.