I would recommend- start with Nightfall (to get exposed to his style) and follow it up with I Robot to set context and dive straight into Foundation. The rest of the Robot series and Foundation sequels can go hand in hand and drop Prelude all the way to the bottom. Lovely topic!
How to Asimov
• I Robot
• The Caves of Steel
• The Naked Sun
• The Robots of Dawn
• Robots and Empire
• The Stars, Like Dust
• The Currents of Space
• Pebble in the Sky
• Prelude to Foundation
• Forward the Foundation
• Foundation
• Foundation and Empire
• Second Foundation
• Foundation’s Edge
• Foundation and Earth