Barcelona has endless restaurants to enjoy during your stay and no visitor will find themselves going hungry! There are restaurants to suit all tastes, from top end culinary masterpieces at the cooking school Hoffman in the Born to traditional hearty Spanish paellas on the beach. Pretty much every world cuisine can be found somewhere in the city; Italian, Japanese, Indian, Spanish (naturally!) and also restaurants dedicated to one speciality, such as snails or octopus.
One important recommendation would be to avoid eating on Las Ramblas, or any establishment with photographs of the food outside! They are orientated towards tourists that the owners assume are just passing through; prices are high and quality is low, with cheap ingredients and heavy use of the microwave.
The Born district is one of the best areas close to the centre for eating out, here you can find some excellent places tucked away in the gorgeous winding streets, plus also many open spaces for sitting outside in warm weather. Eating by the sea is always a pleasure and there are plenty of restaurants specialising in seafood to enjoy the traditional dishes of paella or fideu (rice or noodles with fish, clams, mussels, prawns and more). Barceloneta is the place to head for, where restaurants can be found up on the Passeig Maritim and also right down on the beach.
One of the greatest inventions of eating out in Barcelona is the obligatory menu del día, a rule which means all but the very top end restaurants have to offer an economical three course meal at lunch time. There are some fantastic meals to be had for less than 10 euros, including wine and coffee, with no skimping on taste! Overall, eating out is not hugely expensive, especially for visitors from the UK, and the mark-up on wine is not nearly as heavy as many other countries which helps to keep prices reasonable.
Of course, if you are looking to treat yourself (or others!) there are some truly special venues to be discovered, such as El Xalet up Montjuic which has views over the whole city, or the long established Botafumeiro in Gracia.
Service at 8% is included in the bill so there is no need to add an extra 10% afterwards; of course, if you have enjoyed your meal a few extra euros will always be appreciated.
A good place to find restaurant reviews and recommendations is the following website, where you can search by area or cuisine to find that perfect meal!