Should I Slice Steak Before Cooking Fajitas?

Steak for fajitas should be cooked to rare or medium-rare for the best texture and flavor. Slice thinly, against the grain. Cutting meat against the grain into thin strips shortens the muscle fibers, reducing the amount of work you have to do to chew them, and making even tough cuts taste tender.

Should I cut skirt steak before or after cooking?

To help tenderize flank steak, it is often marinated and cooked by grilling, stir-frying, broiling, or smoking. No matter the cooking method, with or without a marinade, for the most delicious results, you should always cut flank steak across the grain.

Should I cut up my steak before cooking?

A steak is not a bag of juices, nothing significant will leak off of it. It's indeed better to cut in a smaller piece that fits your pan, the whole steak should touch the bottom of the pan otherwise you might have uneven cooking / raw ends. TL;DR: Yes, it's fine to cut meats before cooking.