There are a couple specific places to check for problems.
On the passenger side front of the engine compartment, you will see an evap cannister with hoses going to it. Check each of these hoses, especially at the bends and connections for splits or leaks in the hoses.
Next check under the driver's side on the frame rail, there should be another cannister. Check the hoses to that and the ones that run through the frame. Make sure none of those hoses are split, cracked or disconnected.
And make sure the fuel cap isn't on loose.
P0456-EVAP LEAK MONITOR SMALL LEAK DETECTED (.020)
Leak at Gas Cap
Vehicle History and Service Bulletin Investigation
Visual and Physical Inspection
Verify Evaporative Emission Leak
EVAP Purge Solenoid Operation
Intermittent LDP Monitor Failure
Evaporative Emission Leak Detection
LDP Component Leak