Verified answer

At least some sort of business plan. Find a ~good~ location that you can afford that will mesh with your customer base. Think about inventory - how much, what styles, what customers you want to attract. Along with that goes the "look and feel" of your store, signage, stationary and fixtures. Along with all of that is how much money will be needed to pull it off. Pricing should be at least double what you pay wholesale. Also a second hand store has an added problem of where you are going to find inventory.