The liquor you choose to stock in your bar will depend on which cocktails you plan to serve. This list of essential spirits is a good place to begin as it includes the ingredients needed for the most popular cocktails.
Once you have a solid base, you can then build your stock based on other drinks you may want to make. Look through the recipe collection for ideas and specific recipes you may want to experiment with. Use your personal judgement to decide if you are going to stock everything in these lists or only the essentials to fit your individual taste and budget.
While you are thinking about stocking your new bar, you'll also want to think about essential bar tools.