I found it difficult to get good service and food in Cordoba for being English until I learned Spanish! Make the effort - it gets respect.
Seville is great for food, but dont expect this! even if you can speak spanish, expect to be ignored, served slowly and to receive fairly average at best service. cos in all honesty, 90% of bars are like that, and it's pretty normal. Generally, people don't tip much. Maybe a euro or two if you get good service, Spaniards will never add 5-15% IME. Occasionally it is included automatically, but best in cash to the staff.
Speaking Spanish just means you might understand the specials and recommendations better. generally people are super honest in seville and it's worth listening to what they recommend. when in doubt, get a tapas and try it. Menu of the day is usually a good bet too, and even if the food's average, well you get some booze and a coffee or pudding for about 8 euro. So....
The place on Mendez Pelayo mentioned earlier is probably La Vineria San Telmo. It's in front of jardines de Murillo, on a street behind Santa Maria La Blanca. Expensive but big n decent tapas. Lots of places are good value and decent food however.
I would also recommend:
Bar Catalina (next door to San Telmo)
La Chaparrita (Mexican restaurant on Eduardo Dato, across the road up the bridge and straight on from Santa María La Blanca. Excellent.)
Bar Levies (SHIT service. but fairly cheap and wide selection, some veggie options. food sort of tasty and varied, somewhat basic, but it's a great location. nice outdoor seating. just down the street is La Carboneria for touristy flamenco and piano sing-a-longs, v. fun.)
Los Coloniales (cheap, good grub, very busy usually, 2 locations -- the one up from Encarnación has outdoor seating)
Bodega Santa Cruz Las Columnas (on mateos gago, street up from cathedral into santa cruz. super traditional, great banter, good place for drinks and tapas or montaditos)
La Oveja Negra (in centre near cathedral, good wine)
La Azotea (more expensive, but good tapas. towards alameda)
Eslava (Plaza san lorenzo. posh, small tapas, got a big reputation)
La Chunga (big reputation, great tapas, posh nosh, near plaza de torros)
Las Columnas Alameda (greasy chips and typical unhealthy spanish tapas before posh food came along. get a serranito!)
Casa Paco (Alameda - some great food and outdoor seating. best in the evening but gets busy. good beer on tap for a change, has leffe)
La Madrassa (towards the end of alameda, street off to the right, up past a kebab place on a corner)
Paladar (towards the end of alameda, street off to the left, street from the cop shop. some good fish and veggie-ish options)
Duo Tapas (end of alameda, calle calatrava, some excellent food)
Nikkei (Japanese-Peruvian fusion tapas on Calatrava at the end of Alameda. AMAZING!)
Antojo (Calatrava, at end. apparently not as good as used to be, but ive had some stunning food there. posh nosh).
ConTenedor (On San Luis, posh and expensive, amazing food apparently but i've never been. know people who have)
There are tbh, loads more, and plenty of Sevillanos would never go to some of those places. Not all are typical food, but not all "typical tapas" are always amazing. Some are! Sometimes variety is nice, and jazzed up tapas has hit Sevilla big in the past 10-15 years. I think it's probs one of the best places to eat out in Spain. Far better than Granada and Málaga, IMO. Generally don't expect much understanding or options if you're vegetarian, and if you're strict, RESEARCH online and expect them to try and serve you fish, jamon, chicken etc as veggie options. You need to be quite demanding basically! It is not easy in most places in Seville.
I'll try and make a list of "things to see" but quite busy atm, and lots is already on this thread. DON'T MISS La Alcazar, it's awesome. Going out to Italica in Santiponce is also a good bet if it's not too hot, as there's little shade there. Great restaurant in front that serves big dishes of meat, has a big reputation. Se come bien en santiponce!