Too many Mexican food memories to try to dredge up, but here are a few random ones:
One of the first "good" sit-down Mexican meals I ever had was at a restaurant called Villa Taxco, on Sunset - I think it was between Highland and La Brea, near the IHOP. Not to be confused with Gardens of Taxco just off Santa Monica in West Hollywood, a more eccentric but extremely popular independent place.
Some of the best I had was off a food truck in the industrial section of L.A. when I'd visit a plant we represented. This was way before food trucks became the THING they are now, when they existed to serve workers where there weren't a lot of food places around. This was akin to some of the great street tacos and the like in Mexico itself.
Likewise, other places with the best food were invariably the mom-and-pop joints that were literally everywhere in L.A.
I always think of quesadillas at Oblath's (across from Paramount) which I discovered while walking around when seeing films at the Encore Theater on Melrose. It was the first place I had quesadillas with corn tortillas instead of flour. (Quesadillas and good nachos - real ones, not what people nowadays have been trained to think are nachos - were always favorites, and I'd often make a meal of either or both.)
Another favorite was El Carmen on W. 3rd St. in L.A. I believe it's still there, at least in name. For us in the 1970s and 1980s it was a plain but familiar and affordable Mexican food paradise. Just one in a million hole-in-the-wall jernts, always bustling, always immensely satisfying.