I use a lime juice/worchestershire sauce combo to marinate my fajitas and let them sit from at least 45 minutes to all day.
In Texas I used skirt steak for the fajitas. Now that I'm in Virginia where this cut is not so popular, I often use strips of steak/beef cut for stir fry.
Fajitas have been a passion at my house for over 20 years; now that I'm single I make them with deliberate leftovers so I can have them quickly for lunch.
I also make my own salsa for them.
Jan in VA