Before you sign a thing or hammer a single nail, do some research to check out your potential return on investment. If you're adding bedrooms or bathrooms, for example, this can boost your home's resale value, but by how much?
If you can, find a realtor that you trust, and look at "comps" in your neighborhood. Comps are homes near yours that have the same stats as yours, like the number of bedrooms and bathrooms. Checking out some comps can give you an idea of whether you're sinking more money into your renovation than you'll get back when you eventually sell the house.
Whether you're adding a bathroom, remodeling the kitchen, or replacing carpet with hardwoods, a realtor is your best friend when it comes to sussing out the value of your renovation. He has access to databases of home sales in your area and can tell you what a 2 bedroom/1 bathroom home with an outdated kitchen tends to sell for in your area versus one with an updated kitchen. If homes in your area with wall to wall carpeting are selling for the same prices as similar-sized ones with hardwood floors throughout, you need to decide if you're willing to take the hit to make your house look the way you want.