Ah man, this is such a loaded question!! There are literally TONS of restaurants here that are amazing!! It all depends on how much you really want to spend as some of these restaurants can add up quick! I was in sticker shock when I moved down here!
Make sure you go to Little Italy (near downtown). There are an endless amount of restaurants that are phenomenal! Ketnner Exchange and Juniper and Ivy are on another level, but you pay a pretty penny (celebrity chef owned)! Juniper and Ivy actually has a burger and animal fries that are off the menu that are delicious! In the same area is the Crack Shack. A chicken spot that's a little bit more affordable and casual. It's really good! There's a more casual spot called Carnitas Snack Shack that has two locations that is really glutinous and amazing! There's another awesome (but spendy) restaurant called Coastera that's away from downtown that's really good. They have awesome views on downtown! You also must go to the taco shops! They are cheap and always delicious! If you are a beer drinker, there are tons of breweries to try! Literally google top San Diego breweries and you will have well over 100 spots to choose from! Ballast Point is typically a favorite (even if they sold out)!
For locations, sunset cliffs is amazing! Great place to walk around, jog or just drive! Wind and Sea beach is beautiful. Go to either of these places for sunset!! Also, make sure to explore balboa park. It's huge and amazing!!!