MDI traces must be 50 Ω to ground and 100 Ω-differential controlled impedance.
Route MDI traces to transformer on the same layer.
Use a metal shielded RJ-45 connector, and connect the shield to chassis ground.
Use magnetics with integrated common-mode choking devices.
Void supplies and ground beneath magnetics.
Do not overlap the circuit and chassis ground planes, keep them isolated. Instead, make chassis ground an isolated island and make a void between the chassis and circuit ground. Connecting circuit and chassis planes using a size 1206 resistor and capacitor on either side of the connector is a good practice.