Also, if you want something sweet try Gelatoteca SuSo on Calle Dela Bissa. Their Manet (Gianluca, Pistachio, and salt) was so good!
When I've been there I didn't booked, but I don't know if things have changed lately. I suggest you Trattoria Alla Vedova , the place is great (with copper kettles hanging from the roof) and you can simply have a drink or a pasta, not too expensive (though you don't mind). Or I may suggest you Cantine del Vino Già Schiavi here you can have oysters and fresh fish served with the best wines.
Have a nice stay in Venice!
Pro-tip #1: cicheti - this is the italian word for tapas and you can make a meal out of them. You point at things that look tasty, say "Doo-ay" (two!) and graze away.
Pro-tip #2: Aperol Spritz' abound. They are those orange drinks you see and they are refreshing as hell.
Pro-tip #3: Avoid San Marco Square for food.
Pro-tip #4: Pizza in Venice is weak.
Pro-tip #5: To detect a good gelato place, look at the pistachio flavor. If it's bright green, find another one. Should be a duller grayish-green.
As for places to go:
Ostaria dei Zemei - Great cicheti.
Osteria all'Arco - More cicheti.
Al Merca' - More. Cicheti.
Bancogiro - More.
Alfredo‘s - Fresh Pasta To Go and Gelati - delish for cheap/quick pasta. Somewhat hard to find, like everything in Venice.
Venice is not necessarily known for great food, so I'd save your fancy dining energy for other parts of your trip.
I really like A beccafico for a nice meal. I've had pizza and pasta for a late lunch/early dinner that was amazing. Good service. Right on Campo San Stefano which is a cool square with good people watching. They cap of a meal their with different types of digestif's, I had what I would call a canteloupe-cello (like a limoncello but with canteloupe) that was spectacular.
We used Trip Advisor while we were in Venice for food suggestions! It never let us down!