Always remember the following: Air, Fuel, Spark and Compression when it comes time to diagnose a problem with your Mustang. Seeing that you're new to Mustangs and if you want to do the work yourself I suggest the following web site for testing procedures:
http://easyautodiagnostics.com/ford/4.9L-5.0L-5.8L/index-of-articles-1
The members here are also a source of information. If you take your time to read and re-read you should be fine. If you can't find your answer, then posting a question is always best. I'm not sure what tools or test equipment you have but with the web site above, I'm going to recommend a Chilton's Manual for your car.
http://www.amazon.com/Ford-Mustang-through-Updated-Chiltons/dp/1563926490
To check your injectors, I like using a noid light:
http://easyautodiagnostics.com/misc-index/noid-light-tool-review-1
To check for spark use a spark tester:
http://www.autozone.com/test-scan-a...oem-in-line-ignition-spark-tester/900800_0_0/
So back to the Four main things you need for an engine: Air: unless you have a towel stuck in your inlet you have Air. Fuel: Use the noid light, it's easier and safer to check if your fuel injectors are pulsing. Spark: Safer to use the spark tester to verify you have spark. Compression: unless the engine is really worn out but I'm going to assume it's fine. But a simple compression check can verify if compression is okay.
Timing: Do you know how to check your initial timing? Do you have a timing light?
I know that's a lot to digest but let's leave it there until you can confirm you're getting fuel and spark.
Good luck
Michael Plummer