Honestly, one of the best spots to open a bar is exactly where a bar used to be. I would do specs on the previous area though, make sure that they havent been out of business for too long and its important to see how long they were in business for. This piggy back effect brings you business from the start. (as long as the ending for the previous bar wasnt too unfortunate, - you will find yourself meeting the local regulars of that bar, curious to see what youve done with the place) Likewise; you might move closer to a popular bar so you receive the run off from people who dont want to wait when they are at peak hours.

Just some general ideas. Hope thats helpful :0