Don't.
(I suppose I should elaborate on that? But I really hated Brussles. Other Forum members warned me. It is just a big dirty city. Scummy ponds, graffiti-covered buildings, un-swept streets, crowds of tourists and locals. And we had our cell phone stolen.
However, if you do go to Brussels:
We stayed at the Brussels Hotel Welcome. It is highly touted in the RS guide and their website makes the rooms look like foreign fantasies, each decorated to reflect a different country. The price is reasonable. But it's 30 years old and shows its age. There are dings in the paint, crud around the the faucets, and the doors aren't soundproof. The non-smoking hotel has a smoking area just down the hall from the Vietnam room. The halls are claustrophobic, and the lobby is piled to the rafters with junk. The complimentary breakfast was just barely edible--with flies settling on the pastries and open jam jars. It was not without redemption: the little window boxes with flowers were lovely, our rooms looked out over a nice quiet street, and the unique memorabilia in the rooms was fascinating (my son stayed in Kenya and loved it). To give credit where it is due, the people who run the place--a man and his wife, their daughter, and a lovely receptionist named Jen--couldn't have been nicer. They gave advice about where to eat, made reservations, helped us report our stolen cell phone to the police, called taxis for us, and were always smiling and friendly when we arrived or departed. All they need to do is clean the place up and it would be a great place to stay.
As to where to eat, my review is equally depressing. RS recommends a place in St. Catherine called La Villette Restaurant. He says it is a "romantic, subdued alternative" with a proud chef and charming interior, facing a small square. We dropped by one night about 9:30 to be told by the hostess/owner that even though the sign said they served until 10:30, they were closing early. They could not seat us--although there were about 6 tables still full. So we made a point of making a reservation for the next evening at 8, but when we arrived and asked for a table inside, were told that they weren't serving inside that evening. I mentioned that I have asthma and the cigarette smokers at the patio tables would be dangerous for me, but the same woman said she couldn't help that. We never did eat there, and I have no hesitation at discouraging others from doing so. The charming little square across from the restaurant was where we had our cell phone stolen off a park bench, by the way.
However, Jen at the Hotel Welcome recommended Le Boussole (not listed in RS, but should be), just down the street. It was very nice--good food, good service, good prices.