Start with your fuel nozzle, see if it's plugged. Check your spray pattern. (Use compressed air at the inlet and see.)
Check your rigging on the FCU, make sure the needle is right at 30 degrees when the throttle is at idle, although if it starts well at subsequent starts, it is probably fine.
Bleed the fuel system.
Check the fuel flow. With the throttle open, motor the engine, (with the ignitor circuit breaker pulled) and check the flow in 15 seconds. I don't recall the numbers off the top of my head, but the Rolls Royce 250 Maintenance Manual in chapter 71 will tell you what the number is supposed to be.