Admittedly, we didn't actually plan very much here - at least, not in a formal way with a written budget or anything. Once we committed to doing it ourselves, that obviously helped save money in labor payments (consider the "sweat equity" as an investment).
But, before you start any remodeling project, it's important to set a budget to help you plan and prioritize your expenses. Decide how much money you can realistically afford to spend on the project, and consider factors such as the cost of materials, labor, and any appliances or fixtures you may need to purchase.
Also consider how long the project will take, and that you'll be able to manage when and how much money you spend. Essentially, you can slow the pace of the project to let that next paycheck come in. With a contractor, you might not have that level of spending control - obviously they'll want to be paid for work delivered.