There are basically two kinds of tacos that I believe in. There's the Tex-Mex version, which most Americans refer to as tacos, that I make with seasoned ground beef (Ortega makes a pretty good taco seasoning), shredded lettuce, grated cheddar cheese, diced tomatoes, and a dollop or two of sour cream, all in either a hard or soft tortilla shell.
Then there's traditional Mexican street tacos, which I frequently buy around here or make myself, consisting of carne asada (seasoned beef) or carnitas (seasoned pork), though I've had some made with beef brisket that were just to die for. This goes on a couple of small, soft corn tortillas and are topped with cilantro, diced onions, and salsa, and sometimes some grated Mexican queso.
Squirrel?! I'll take pretty much any *normal* meat on tacos. Steak, chicken, beef, hamburger, etc.. Often, I use leftover steak or chicken that has already been flavored on a previous meal. It's particularly better if it was something that I grilled cuz that nice smoky taste. I will use whatever cheese I have handy with the exception of American...yuck.
Pico de gallo, consisting of jalepeno, tomatoes, onion, cilantro (I take it easy with that since it tastes like soap to me, but for others I add it), lime and salt. Not traditional but I do like to add some black beans and corn if I have them available.
Topped with lettuce. Sorry, traditionalists. I just like it.
If I don't have what I need for that, I'll make due with just tomatoes, onion, lettuce and maybe salsa.
ETA: This is pretty much the American way. Traditional tacos I have had courtesy of my sister are an entirely different affair.
I have always considered Tacos open to interpretation.
Sometimes I cook a pork roast in my instant pot and season it with pork broth, cumin, chili powder, chipotle powder, fresh garlic, fresh onion, fresh oregano, fresh cilantro (cilantro optional) and salt and pepper. When it's cooked, I shred the pork and fry it in a cast iron frying pan to get crispy parts on it. I usually serve this with steamed corn tortillas, shredded cabbage, mango salsa, tomatoes, avocado with crumbled queso fresco or queso añejo. You can generally find Mexican cheeses in the same area as cottage or ricotta cheese.
A different day, it's wash, rinse repeat but instead of using a pork roast I use a beef roast and beef broth. A cheap cut is fine because you're going to pressure or slow cook it and then shred it. For this one I fry the corn tortillas and fold them like a traditional taco. Instead of shredded cabbage I use shredded lettuce and instead of crumbled queso I use a combo of jack and cheddar cheese that is finely grated.
Instead of a roast you can use ground beef or ground chicken or shredded chicken.
My key "go to" spices for any kind of taco are ground cumin, chili powder, ground annatto, garlic powder, onion powder and sometimes if I want a bit more heat, chipotle chili powder.
As a topping, consider a black bean and corn salsa.