I will work with you to plan the best course of action - lets say that you need your home to sell in order to purchase a new one. A few considerations - you are likely to get a much better deal on your new home and you Should you listing your current home prior to scouring the market for a new home. Both have their risks and rewards. If you're going to apply for a mortgage, selling first is a must, but it also means you may need to find a temporary place to live, or find a new home to buy in a limited time frame. However, a plus to selling first is that it gives you greater leverage when dealing with sellers - if you have a house on the market or even better, under contract, you have a greater chance of negotiating the price of your dream home.
Really, there is no specific order in which things have to be done. Each client's situation is different and taken care of on a case to case basis.