First of all, decide the purpose for which the end table would be used. You may want to place a fancy flower vase or some other decorative item on top of it. If nothing else would be kept along with such items, then you can go for something that is not too big. However, if you are planning to keep items of regular use such as magazines, remotes, pens, notepads, etc. atop the table, then you require something that is large enough for holding them and also the things which would stay on its top all the time.
Think you need some extra space every now and then? You may want to consider buying a nest of end tables. Some end tables are also made in such a way that can actually slide halfway under the couch that they lie next to. This will make it easier for you to reach the items kept on it. If you cannot find one with such a design in the market, you can even get a made to order furniture in Berkshire.
While making different considerations, you must also take height into account as an important factor. Note the height of your couch’s arms and search for something whose top is at the same height. This way, you would not have to struggle and bend over the sofa arms for grabbing the TV remote or coffee cup kept on top of the table.
Last but not the least, keep in mind that there must be a clearance of at least two feet around the end table after you have placed it in position. If you are keeping a lamp on top of it, make sure that there is a wall socket close to the place where you can connect the lamp without any difficulty.