Raise the couch. Use crates, bricks, cement blocks, books or any other sturdy supportive items you can find. Lift the couch so that if you're sitting down, the table is at the level of your chest.
Lower the table, if lifting the couch is not an option. You can shorten the table legs or remove them altogether, and then balance the table on an alternate surface. This could be items such as storage trunks, boxes, books, crates, bricks or cement blocks.
Protect the couch. If you're going to use your couch in place of chairs at your table, make sure the couch covering is resistant to food stains. Use a stain protector on the couch's material, or purchase a removable cover that you use exclusively during meal time.
Clean up immediately after. Once meal time is finished, search the couch diligently for any food stains that might have been left behind. Blot and remove them immediately to ensure that stains won't set. If you're using a removable cover, throw it in the washing machine right after eating so it will be ready for the next use.
Protect yourself. No matter how high the couch is or how low the table, there will likely be a noticeable gap between the table and your lap if you're using the couch to eat. Protect your clothing during meal time by either wearing clothing that's washable, covering yourself with a napkin or a bib, or balancing your plate in your hand.
Protect the floor. Using a couch to sit at the table will virtually guarantee that food will fall on the floor. If you're eating over a carpet, put plastic down under the table before each meal, and vacuum right after. If you're eating over a floor, sweep as soon as the meal is finished. If you're eating over a rug, consider removing the rug, or just rolling back the portion under the table while you're eating.