Joe is right..........Air, Fuel, and Spark.........and the spark has to be in the right order and at the right time.
Here is a good link for timing the 5.0L EFI engines:
http://sbftech.com/index.php/topic,7114.0.html
First and foremost make sure that you are getting spark. If not it could be a bad TFI module, bad ground, or other basic wiring issue. Then make sure it is not 180 degrees off (you're at TDC on the compression stroke of #1, not the exhaust), that you didn't wire up the cap wrong if you took the wires off (either wired in wrong pattern or wrong direction), and that you disconnect the spout when you are setting the base timing.