Say you want a gazebo built. Before calling contractors, define just what you want, on paper. Visit some examples. Print some pictures from the internet. Make a sketch or your yard to scale and show the footprint and the drip line. Will you need grading? How will it be supported, foundation, posts in the ground, posts in concrete? What will keep it in your yard in a windstorm? Do you want electricity? How about a path or at least a stepping stone at the entrance, and maybe some landscaping?

Having all this as resolved as you can will make the rest of the process go much better.