Skirt steak is one of my personal favourites. You won't find it in the supermarket, but a good butcher will get it for you. It is known in France as bavette d'aloyau, but be careful as bavette is usually flank steak. Skirt is the well grained steak that is often used in Mexican and Chineses cooking.
Below is a picture of a beautiful Irish grass fed dry aged skirt steak from Des Savage Butchers in Carlingford, Co. Louth.
Skirt steak should be trimmed to remove all sinew and silverskin. I then usually cut it into nice neat squared off steaks about 15cm long. Some of these will be thicker than others. You can marinate skirt steak, but it is not very tough in my experience. Skirt steak should be cooked hot and fast directly over intense heat. This is not a steak that tastes good if it is well done. Keep it medium at most and use lots of salt.
Since this is a flavoursome cut of beef it can easily handle the punch of our peppery and aromatic Steak rub, and in my opinion it needs it.
One of the biggest changes of mind I have ever had is about seasoning steak. I heard so many chefs and butchers say "a good steak just needs salt and pepper" that I always held it to be true. It is not. They are wrong. A truly good dry rub makes a good steak amazing, and all the more beefy. I wouldn't use a rub on fillet as it is delicate and the flavour is waifish and illusive, but on a robust cut like skirt you should try a rubust seasoning.