Recipe(tried): The Best Marinade (for skirt steak - using lime and jalapenos)

The best and most simple marinade is for every pound of skirt steak (use only skirt steak)

salt and ground black pepper
2 limes (per lb of meat)
2 jalapeno peppers, chopped finely (per lb of meat)

Use an oversize Ziploc bag (1 or 2 gallon bags work). Lay all the meat flat and together, no over lapping.

Shake a reasonable amount of salt and pepper into the bag.

Mix the juice from the limes with the jalapenos. Dump that in the bag and get all the air out as best you can.

Marinade for up to 4 days flipping the bag over every day.

Grill to your liking.