In a prelude for Foundation Asimov revealed his preferred way to tell the story of the universe he created. This list has Asimov's preferred order to read the books in a way that accentuates the story line and overall storytelling.

ROBOTS SERIES

I, Robot
The rest of the Robots
Robot dreams
The Caves of steel
The Naked Sun
The Robots of dawn
Robota and empire

FOUNDATION
Prelude to Foundation
Forward to Foundation
Foundation
Foundation and Empire
Foundation's edge
Foundation and earth

FOUNDATION EXPANDED UNIVERSE
I, Robot
The rest of the Robots
Robot dreams
The Caves of steel
The Naked Sun
The Robots of dawn
Robota and empire
The Stars Like Dust
The Currents of Space
Pebble in the Sky
Prelude to Foundation