User defined - You should first establish a goal that your website is trying to achieve. It is then important to think about who the website is being created for, the users who will be using the website are the most important link. A good way to plan for this is to set up interviews with potential users.
Site maps - Once you figure out what the site is going to do and who it is going to be used for, you can start looking at what info is going to be provided, how it is going to be accessed, and how it is going to be displayed. Site maps are a great way to do this as they let you explore process flows and user paths that could be potentially used. You can start this stage by sketching which will allow you to get a good but easily changeable plan down before you start coding and designing.
Wireframes - Wireframes are a key tool for working out interaction design and an excellent tool for interaction designers to have. Wireframes to a designer are essentially like a blueprint, they help you get everything planned and figured out when it comes to how the user will interact with a site. They allow us to communicate ideas through a visual medium making things easier to explain and plan for.